Update Grape from 0.13.0 to 0.15.0.

Changelog: https://github.com/ruby-grape/grape/blob/v0.15.0/CHANGELOG.md

Works toward #18226.

Gemfile

@@ -69,7 +69,7 @@ gem 'gollum-rugged_adapter', '~> 0.4.2', require: false
 gem 'github-linguist', '~> 4.7.0', require: 'linguist'
 
 # API
-gem 'grape',        '~> 0.13.0'
+gem 'grape',        '~> 0.15.0'
 gem 'grape-entity', '~> 0.4.2'
 gem 'rack-cors',    '~> 0.4.0', require: 'rack/cors'
 

Gemfile.lock

@@ -308,7 +308,7 @@ GEM
       json
       multi_json
       request_store (>= 1.0)
-    grape (0.13.0)
+    grape (0.15.0)
       activesupport
       builder
       hashie (>= 2.1.0)
@@ -876,7 +876,7 @@ DEPENDENCIES
   gollum-lib (~> 4.2)
   gollum-rugged_adapter (~> 0.4.2)
   gon (~> 6.1.0)
-  grape (~> 0.13.0)
+  grape (~> 0.15.0)
   grape-entity (~> 0.4.2)
   hamlit (~> 2.5)
   health_check (~> 2.1.0)