Update to Ruby 2.7 (heroku#86)

And update dependencies using:
`bundle update --minor`

And update sdoc to v2, to fix json deprecation warnings.

Closes heroku#83.
GUS-W-9952834.

Author: edmorley

Gemfile.lock

@@ -1,168 +1,159 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    actioncable (5.2.3)
-      actionpack (= 5.2.3)
+    actioncable (5.2.6)
+      actionpack (= 5.2.6)
       nio4r (~> 2.0)
       websocket-driver (>= 0.6.1)
-    actionmailer (5.2.3)
-      actionpack (= 5.2.3)
-      actionview (= 5.2.3)
-      activejob (= 5.2.3)
+    actionmailer (5.2.6)
+      actionpack (= 5.2.6)
+      actionview (= 5.2.6)
+      activejob (= 5.2.6)
       mail (~> 2.5, >= 2.5.4)
       rails-dom-testing (~> 2.0)
-    actionpack (5.2.3)
-      actionview (= 5.2.3)
-      activesupport (= 5.2.3)
-      rack (~> 2.0)
+    actionpack (5.2.6)
+      actionview (= 5.2.6)
+      activesupport (= 5.2.6)
+      rack (~> 2.0, >= 2.0.8)
       rack-test (>= 0.6.3)
       rails-dom-testing (~> 2.0)
       rails-html-sanitizer (~> 1.0, >= 1.0.2)
-    actionview (5.2.3)
-      activesupport (= 5.2.3)
+    actionview (5.2.6)
+      activesupport (= 5.2.6)
       builder (~> 3.1)
       erubi (~> 1.4)
       rails-dom-testing (~> 2.0)
       rails-html-sanitizer (~> 1.0, >= 1.0.3)
-    activejob (5.2.3)
-      activesupport (= 5.2.3)
+    activejob (5.2.6)
+      activesupport (= 5.2.6)
       globalid (>= 0.3.6)
-    activemodel (5.2.3)
-      activesupport (= 5.2.3)
-    activerecord (5.2.3)
-      activemodel (= 5.2.3)
-      activesupport (= 5.2.3)
+    activemodel (5.2.6)
+      activesupport (= 5.2.6)
+    activerecord (5.2.6)
+      activemodel (= 5.2.6)
+      activesupport (= 5.2.6)
       arel (>= 9.0)
-    activestorage (5.2.3)
-      actionpack (= 5.2.3)
-      activerecord (= 5.2.3)
-      marcel (~> 0.3.1)
-    activesupport (5.2.3)
+    activestorage (5.2.6)
+      actionpack (= 5.2.6)
+      activerecord (= 5.2.6)
+      marcel (~> 1.0.0)
+    activesupport (5.2.6)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
     arel (9.0.0)
-    bootsnap (1.7.3)
+    bootsnap (1.9.1)
       msgpack (~> 1.0)
-    builder (3.2.3)
+    builder (3.2.4)
     coffee-rails (4.2.2)
       coffee-script (>= 2.2.0)
       railties (>= 4.0.0)
     coffee-script (2.4.1)
       coffee-script-source
       execjs
     coffee-script-source (1.12.2)
-    concurrent-ruby (1.1.5)
-    crass (1.0.5)
-    erubi (1.8.0)
-    execjs (2.7.0)
-    ffi (1.15.0)
-    globalid (0.4.2)
-      activesupport (>= 4.2.0)
-    i18n (1.6.0)
+    concurrent-ruby (1.1.9)
+    crass (1.0.6)
+    erubi (1.10.0)
+    execjs (2.8.1)
+    ffi (1.15.4)
+    globalid (0.5.2)
+      activesupport (>= 5.0)
+    i18n (1.8.10)
       concurrent-ruby (~> 1.0)
-    jbuilder (2.7.0)
-      activesupport (>= 4.2.0)
-      multi_json (>= 1.2)
-    jquery-rails (4.3.1)
+    jbuilder (2.11.2)
+      activesupport (>= 5.0.0)
+    jquery-rails (4.4.0)
       rails-dom-testing (>= 1, < 3)
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
-    json (1.8.6)
-    listen (3.5.0)
+    listen (3.7.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
-    loofah (2.3.1)
+    loofah (2.12.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
     mail (2.7.1)
       mini_mime (>= 0.1.1)
-    marcel (0.3.3)
-      mimemagic (~> 0.3.2)
+    marcel (1.0.2)
     method_source (0.9.2)
-    mimemagic (0.3.9)
-      nokogiri (~> 1)
-      rake
-    mini_mime (1.0.2)
+    mini_mime (1.1.2)
     mini_portile2 (2.6.1)
-    minitest (5.11.3)
+    minitest (5.14.4)
     msgpack (1.4.2)
-    multi_json (1.13.1)
     nio4r (2.5.8)
     nokogiri (1.12.5)
       mini_portile2 (~> 2.6.1)
       racc (~> 1.4)
     pg (0.21.0)
-    puma (4.3.9)
+    puma (4.3.10)
       nio4r (~> 2.0)
     racc (1.5.2)
     rack (2.2.3)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
-    rails (5.2.3)
-      actioncable (= 5.2.3)
-      actionmailer (= 5.2.3)
-      actionpack (= 5.2.3)
-      actionview (= 5.2.3)
-      activejob (= 5.2.3)
-      activemodel (= 5.2.3)
-      activerecord (= 5.2.3)
-      activestorage (= 5.2.3)
-      activesupport (= 5.2.3)
+    rails (5.2.6)
+      actioncable (= 5.2.6)
+      actionmailer (= 5.2.6)
+      actionpack (= 5.2.6)
+      actionview (= 5.2.6)
+      activejob (= 5.2.6)
+      activemodel (= 5.2.6)
+      activerecord (= 5.2.6)
+      activestorage (= 5.2.6)
+      activesupport (= 5.2.6)
       bundler (>= 1.3.0)
-      railties (= 5.2.3)
+      railties (= 5.2.6)
       sprockets-rails (>= 2.0.0)
     rails-dom-testing (2.0.3)
       activesupport (>= 4.2.0)
       nokogiri (>= 1.6)
-    rails-html-sanitizer (1.2.0)
-      loofah (~> 2.2, >= 2.2.2)
-    railties (5.2.3)
-      actionpack (= 5.2.3)
-      activesupport (= 5.2.3)
+    rails-html-sanitizer (1.4.2)
+      loofah (~> 2.3)
+    railties (5.2.6)
+      actionpack (= 5.2.6)
+      activesupport (= 5.2.6)
       method_source
       rake (>= 0.8.7)
       thor (>= 0.19.0, < 2.0)
     rake (12.3.3)
-    rb-fsevent (0.10.4)
+    rb-fsevent (0.11.0)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rdoc (4.3.0)
-    sass (3.5.5)
+    rdoc (6.3.2)
+    sass (3.7.4)
       sass-listen (~> 4.0.0)
     sass-listen (4.0.0)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
-    sass-rails (5.0.7)
-      railties (>= 4.0.0, < 6)
+    sass-rails (5.1.0)
+      railties (>= 5.2.0)
       sass (~> 3.1)
       sprockets (>= 2.8, < 4.0)
       sprockets-rails (>= 2.0, < 4.0)
       tilt (>= 1.1, < 3)
-    sdoc (0.4.2)
-      json (~> 1.7, >= 1.7.7)
-      rdoc (~> 4.0)
-    spring (2.0.2)
-      activesupport (>= 4.2)
+    sdoc (2.2.0)
+      rdoc (>= 5.0)
+    spring (2.1.1)
     sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
-    sprockets-rails (3.2.1)
+    sprockets-rails (3.2.2)
       actionpack (>= 4.0)
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
     thor (0.20.3)
     thread_safe (0.3.6)
-    tilt (2.0.8)
-    turbolinks (5.1.0)
-      turbolinks-source (~> 5.1)
-    turbolinks-source (5.1.0)
-    tzinfo (1.2.5)
+    tilt (2.0.10)
+    turbolinks (5.2.1)
+      turbolinks-source (~> 5.2)
+    turbolinks-source (5.2.0)
+    tzinfo (1.2.9)
       thread_safe (~> 0.1)
-    uglifier (4.1.4)
+    uglifier (4.2.0)
       execjs (>= 0.3.0, < 3)
-    websocket-driver (0.7.1)
+    websocket-driver (0.7.5)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.5)
 
@@ -185,7 +176,7 @@ DEPENDENCIES
   uglifier
 
 RUBY VERSION
-   ruby 2.6.6p146
+   ruby 2.7.4p191
 
 BUNDLED WITH
-   2.2.15
+   2.2.28