Bump loofah from 2.2.3 to 2.3.1 (heroku#57)

Bumps [loofah](https://github.com/flavorjones/loofah) from 2.2.3 to 2.3.1.
- [Release notes](https://github.com/flavorjones/loofah/releases)
- [Changelog](https://github.com/flavorjones/loofah/blob/master/CHANGELOG.md)
- [Commits](flavorjones/loofah@v2.2.3...v2.3.1)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Gemfile.lock

@@ -54,7 +54,7 @@ GEM
       execjs
     coffee-script-source (1.12.2)
     concurrent-ruby (1.1.5)
-    crass (1.0.4)
+    crass (1.0.5)
     erubi (1.8.0)
     execjs (2.7.0)
     ffi (1.9.18)
@@ -74,7 +74,7 @@ GEM
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
       ruby_dep (~> 1.2)
-    loofah (2.2.3)
+    loofah (2.3.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
     mail (2.7.1)
@@ -89,7 +89,7 @@ GEM
     msgpack (1.3.1)
     multi_json (1.13.1)
     nio4r (2.5.1)
-    nokogiri (1.10.4)
+    nokogiri (1.10.5)
       mini_portile2 (~> 2.4.0)
     pg (0.19.0)
     puma (3.11.2)