Use oj gem for faster JSON processing

It's mainly intended to improve Elasticsearch indexing performance
(through multi_json gem), but other gems could benefit from it too, like
grape.

CHANGELOG

@@ -168,6 +168,7 @@ v 8.11.5
   - Scope webhooks/services that will run for confidential issues
   - Remove gitorious from import_sources
   - Fix confidential issues being exposed as public using gitlab.com export
+  - Use oj gem for faster JSON processing
 
 v 8.11.4
   - Fix resolving conflicts on forks. !6082

Gemfile

@@ -206,6 +206,9 @@ gem 'mousetrap-rails', '~> 1.4.6'
 # Detect and convert string character encoding
 gem 'charlock_holmes', '~> 0.7.3'
 
+# Faster JSON
+gem 'oj', '~> 2.17.4'
+
 # Parse time & duration
 gem 'chronic', '~> 0.10.2'
 gem 'chronic_duration', '~> 0.10.6'

Gemfile.lock

@@ -427,6 +427,7 @@ GEM
       rack (>= 1.2, < 3)
     octokit (4.3.0)
       sawyer (~> 0.7.0, >= 0.5.3)
+    oj (2.17.4)
     omniauth (1.3.1)
       hashie (>= 1.2, < 4)
       rack (>= 1.0, < 3)
@@ -904,6 +905,7 @@ DEPENDENCIES
   nokogiri (~> 1.6.7, >= 1.6.7.2)
   oauth2 (~> 1.2.0)
   octokit (~> 4.3.0)
+  oj (~> 2.17.4)
   omniauth (~> 1.3.1)
   omniauth-auth0 (~> 1.4.1)
   omniauth-azure-oauth2 (~> 0.0.6)