Upgrade oauth2 from 1.0.0 to 1.2.0.

Changelog: https://github.com/intridea/oauth2/compare/v1.0.0...v1.2.0

Follow-up on !3434 since 1.2.0 doesn't limit the JWT version we can use.

Gemfile

@@ -339,7 +339,7 @@ gem 'activerecord-session_store', '~> 1.0.0'
 gem "nested_form", '~> 0.3.2'
 # OAuth
-gem 'oauth2', '~> 1.0.0'
+gem 'oauth2', '~> 1.2.0'
 # Soft deletion
 gem "paranoia", "~> 2.0"

Gemfile.lock

@@ -355,7 +355,7 @@ GEM
     jquery-ui-rails (5.0.5)
       railties (>= 3.2.16)
     json (1.8.3)
-    jwt (1.5.2)
+    jwt (1.5.4)
     kaminari (0.17.0)
       actionpack (>= 3.0.0)
       activesupport (>= 3.0.0)
@@ -395,7 +395,7 @@ GEM
     mini_portile2 (2.1.0)
     minitest (5.7.0)
     mousetrap-rails (1.4.6)
-    multi_json (1.11.2)
+    multi_json (1.12.1)
     multi_xml (0.5.5)
     multipart-post (2.0.0)
     mysql2 (0.3.20)
@@ -408,12 +408,12 @@ GEM
       pkg-config (~> 1.1.7)
     numerizer (0.1.1)
     oauth (0.4.7)
-    oauth2 (1.0.0)
+    oauth2 (1.2.0)
       faraday (>= 0.8, < 0.10)
       jwt (~> 1.0)
       multi_json (~> 1.3)
       multi_xml (~> 0.5)
-      rack (~> 1.2)
+      rack (>= 1.2, < 3)
     octokit (4.3.0)
       sawyer (~> 0.7.0, >= 0.5.3)
     omniauth (1.3.1)
@@ -898,7 +898,7 @@ DEPENDENCIES
   net-ssh (~> 3.0.1)
   newrelic_rpm (~> 3.14)
   nokogiri (~> 1.6.7, >= 1.6.7.2)
-  oauth2 (~> 1.0.0)
+  oauth2 (~> 1.2.0)
   octokit (~> 4.3.0)
   omniauth (~> 1.3.1)
   omniauth-auth0 (~> 1.4.1)