Re-add mysql2 to the Gemfile.lock

Changelog.md

+# 0.5.10.1
+
+We made a mistake and removed `mysql2` from the `Gemfile.lock` in a recent gem update. Since this could cause some issues for some installations, we decided to release a hotfix.
+
 # 0.5.10.0
 
 ## Refactor

Gemfile.lock

@@ -474,6 +474,7 @@ GEM
     multi_test (0.1.2)
     multi_xml (0.5.5)
     multipart-post (2.0.0)
+    mysql2 (0.4.4)
     naught (1.1.0)
     nenv (0.3.0)
     nested_form (0.3.2)
@@ -516,7 +517,6 @@ GEM
     orm_adapter (0.5.0)
     parser (2.3.1.2)
       ast (~> 2.2)
-    pg (0.18.4)
     phantomjs (2.1.1.0)
     pkg-config (1.1.7)
     powerpack (0.1.1)
@@ -846,6 +846,7 @@ DEPENDENCIES
   mini_magick (= 4.5.1)
   minitest
   mobile-fu (= 1.3.1)
+  mysql2 (= 0.4.4)
   nokogiri (= 1.6.8)
   omniauth (= 1.3.1)
   omniauth-facebook (= 3.0.0)
@@ -853,7 +854,6 @@ DEPENDENCIES
   omniauth-twitter (= 1.2.1)
   omniauth-wordpress (= 0.2.2)
   open_graph_reader (= 0.6.1)
-  pg (= 0.18.4)
   pry
   pry-byebug
   quiet_assets (= 1.1.0)