Upgrade gem mysql2 from 0.2.7 to 0.3.11 as the former doesn't work with Rails 3.2 anymore.

Gemfile

@@ -3,7 +3,7 @@ source 'http://rubygems.org'
 
 gem 'rails', '3.2.3'
 
-gem 'mysql2', '0.2.7'
+gem 'mysql2', '0.3.11'
 gem 'activeadmin', '0.4.0'
 
 # https://github.com/plataformatec/devise

Gemfile.lock

@@ -106,7 +106,7 @@ GEM
     multi_json (1.0.4)
     multi_xml (0.2.2)
     multipart-post (1.1.5)
-    mysql2 (0.2.7)
+    mysql2 (0.3.11)
     net-scp (1.0.4)
       net-ssh (>= 1.99.1)
     net-sftp (2.0.5)
@@ -184,7 +184,7 @@ DEPENDENCIES
   coffee-rails (= 3.2.2)
   devise (= 2.0.4)
   mail
-  mysql2 (= 0.2.7)
+  mysql2 (= 0.3.11)
   rails (= 3.2.3)
   sass-rails (= 3.2.5)
   twitter (= 1.6.0)