Merge branch 'update-omniauth-1-3-1' into 'master'

Update omniauth to 1.3.1 for memory performance

OmniAuth 1.3.1 may improve memory performance (~ 70% according to [intridea/omniauth!774](https://github.com/intridea/omniauth/pull/774)).

Closes #2404.

See merge request !2805

Gemfile

@@ -21,7 +21,7 @@ gem "pg", '~> 0.18.2', group: :postgres
 gem 'devise',                 '~> 3.5.4'
 gem 'devise-async',           '~> 0.9.0'
 gem 'doorkeeper',             '~> 2.2.0'
-gem 'omniauth',               '~> 1.2.2'
+gem 'omniauth',               '~> 1.3.1'
 gem 'omniauth-azure-oauth2',  '~> 0.0.6'
 gem 'omniauth-bitbucket',     '~> 0.0.2'
 gem 'omniauth-cas3',          '~> 1.1.2'

Gemfile.lock

@@ -491,9 +491,9 @@ GEM
       rack (~> 1.2)
     octokit (3.8.0)
       sawyer (~> 0.6.0, >= 0.5.3)
-    omniauth (1.2.2)
+    omniauth (1.3.1)
       hashie (>= 1.2, < 4)
-      rack (~> 1.0)
+      rack (>= 1.0, < 3)
     omniauth-azure-oauth2 (0.0.6)
       jwt (~> 1.0)
       omniauth (~> 1.0)
@@ -963,7 +963,7 @@ DEPENDENCIES
   nprogress-rails (~> 0.1.6.7)
   oauth2 (~> 1.0.0)
   octokit (~> 3.8.0)
-  omniauth (~> 1.2.2)
+  omniauth (~> 1.3.1)
   omniauth-azure-oauth2 (~> 0.0.6)
   omniauth-bitbucket (~> 0.0.2)
   omniauth-cas3 (~> 1.1.2)