Bump octokit to `~> 3.8.0`

Closes #2877

Gemfile

@@ -301,7 +301,7 @@ end
 gem "newrelic_rpm", '~> 3.9.4.245'
 gem 'newrelic-grape'
-gem 'octokit', '~> 3.7.0'
+gem 'octokit', '~> 3.8.0'
 gem "mail_room", "~> 0.6.1"

Gemfile.lock

@@ -492,7 +492,7 @@ GEM
       multi_json (~> 1.3)
       multi_xml (~> 0.5)
       rack (~> 1.2)
-    octokit (3.7.1)
+    octokit (3.8.0)
       sawyer (~> 0.6.0, >= 0.5.3)
     omniauth (1.2.2)
       hashie (>= 1.2, < 4)
@@ -965,7 +965,7 @@ DEPENDENCIES
   nokogiri (= 1.6.7.1)
   nprogress-rails (~> 0.1.6.7)
   oauth2 (~> 1.0.0)
-  octokit (~> 3.7.0)
+  octokit (~> 3.8.0)
   omniauth (~> 1.2.2)
   omniauth-azure-oauth2 (~> 0.0.6)
   omniauth-bitbucket (~> 0.0.2)