Upgrade acts-as-taggable-on from 3.5.0 to 4.0.0.

Changelog: https://github.com/mbleigh/acts-as-taggable-on/blob/master/CHANGELOG.md#400--2016-08-08

Gemfile

@@ -130,7 +130,7 @@ gem 'state_machines-activerecord', '~> 0.4.0'
 gem 'after_commit_queue', '~> 1.3.0'
 # Issue tags
-gem 'acts-as-taggable-on', '~> 3.4'
+gem 'acts-as-taggable-on', '~> 4.0'
 # Background jobs
 gem 'sidekiq', '~> 4.2'

Gemfile.lock

@@ -44,8 +44,8 @@ GEM
       minitest (~> 5.1)
       thread_safe (~> 0.3, >= 0.3.4)
       tzinfo (~> 1.1)
-    acts-as-taggable-on (3.5.0)
-      activerecord (>= 3.2, < 5)
+    acts-as-taggable-on (4.0.0)
+      activerecord (>= 4.0)
     addressable (2.3.8)
     after_commit_queue (1.3.0)
       activerecord (>= 3.0)
@@ -802,7 +802,7 @@ DEPENDENCIES
   RedCloth (~> 4.3.2)
   ace-rails-ap (~> 4.1.0)
   activerecord-session_store (~> 1.0.0)
-  acts-as-taggable-on (~> 3.4)
+  acts-as-taggable-on (~> 4.0)
   addressable (~> 2.3.8)
   after_commit_queue (~> 1.3.0)
   akismet (~> 2.0)
@@ -986,4 +986,4 @@ DEPENDENCIES
   wikicloth (= 0.8.1)
 BUNDLED WITH
-   1.13.1
+   1.13.2