Merge branch 'rs-update-doorkeeper' into 'master'

Update doorkeeper to 4.2.0

Changelog: https://git.io/v6PnV

See merge request !5881
(cherry picked from commit c5aa31c8)

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
+v 8.8.9
+  - Upgrade Doorkeeper to 4.2.0. !5881
+
 v 8.8.8
   - Upgrade Rails to 4.2.7.1 for security fixes. !5781
 

Gemfile

@@ -19,7 +19,7 @@ gem "pg", '~> 0.18.2', group: :postgres
 
 # Authentication libraries
 gem 'devise',                 '~> 3.5.4'
-gem 'doorkeeper',             '~> 3.1'
+gem 'doorkeeper',             '~> 4.2.0'
 gem 'devise-async',           '~> 0.9.0'
 gem 'omniauth',               '~> 1.3.1'
 gem 'omniauth-auth0',         '~> 1.4.1'

Gemfile.lock

@@ -172,8 +172,8 @@ GEM
     diff-lcs (1.2.5)
     diffy (3.0.7)
     docile (1.1.5)
-    doorkeeper (3.1.0)
-      railties (>= 3.2)
+    doorkeeper (4.2.0)
+      railties (>= 4.2)
     dropzonejs-rails (0.7.2)
       rails (> 3.1)
     email_reply_parser (0.5.8)
@@ -917,7 +917,7 @@ DEPENDENCIES
   devise-async (~> 0.9.0)
   devise-two-factor (~> 2.0.0)
   diffy (~> 3.0.3)
-  doorkeeper (~> 3.1)
+  doorkeeper (~> 4.2.0)
   dropzonejs-rails (~> 0.7.1)
   email_reply_parser (~> 0.5.8)
   email_spec (~> 1.6.0)