Bump grape 1.4 to 1.5

version 1.4 broke Cache-Control that we rely on
see ruby-grape/grape#2088

Full [Change log](https://github.com/ruby-grape/grape/blob/master/CHANGELOG.md)

Gemfile

@@ -22,7 +22,7 @@ gem 'govuk_template',         '0.26.0'
 gem 'govuk_frontend_toolkit', '~> 8.2.0'
 gem 'govuk_elements_rails',   '~> 3.1.2'
 gem 'govuk_notify_rails',     '~> 2.1.2'
-gem 'grape',                  '~> 1.4.0'
+gem 'grape',                  '~> 1.5.0'
 gem 'grape-entity',           '~> 0.8.1'
 gem 'grape-papertrail',       '~> 0.2.0'
 gem 'grape-swagger',          '~> 1.3.0'

Gemfile.lock

@@ -239,7 +239,7 @@ GEM
     dry-equalizer (0.3.0)
     dry-inflector (0.2.0)
     dry-initializer (3.0.3)
-    dry-logic (1.0.7)
+    dry-logic (1.0.8)
       concurrent-ruby (~> 1.0)
       dry-core (~> 0.2)
       dry-equalizer (~> 0.2)
@@ -310,7 +310,7 @@ GEM
       rails (>= 4.1.0)
     govuk_template (0.26.0)
       rails (>= 3.1)
-    grape (1.4.0)
+    grape (1.5.0)
       activesupport
       builder
       dry-types (>= 1.1)
@@ -810,7 +810,7 @@ DEPENDENCIES
   govuk_frontend_toolkit (~> 8.2.0)
   govuk_notify_rails (~> 2.1.2)
   govuk_template (= 0.26.0)
-  grape (~> 1.4.0)
+  grape (~> 1.5.0)
   grape-entity (~> 0.8.1)
   grape-papertrail (~> 0.2.0)
   grape-swagger (~> 1.3.0)