Bump Sprockets backport to 2.2.2.backport2

Although undocumented, the latest backport should provide feature/fix
parity with 2.10.0. Namely it should support `bower.json` in addition
to deprecated `component.json` manifests.

https://gist.github.com/myabc/9526121#file-gistfile1-diff-L129

Gemfile

@@ -45,7 +45,7 @@ end
 source 'https://rubygems.org'
 
 gem "rails", "~> 3.2.17"
-gem "sprockets", "2.2.2.backport1"
+gem "sprockets", "2.2.2.backport2"
 
 gem "coderay", "~> 1.0.5"
 gem "rubytree", "~> 0.8.3"

Gemfile.lock

@@ -348,7 +348,7 @@ GEM
       simplecov-html (~> 0.7.1)
     simplecov-html (0.7.1)
     slop (3.4.6)
-    sprockets (2.2.2.backport1)
+    sprockets (2.2.2.backport2)
       hike (~> 1.2)
       multi_json (~> 1.0)
       rack (~> 1.0)
@@ -470,7 +470,7 @@ DEPENDENCIES
   shoulda
   shoulda-matchers
   simplecov (>= 0.8.pre)
-  sprockets (= 2.2.2.backport1)
+  sprockets (= 2.2.2.backport2)
   sqlite3
   strong_parameters
   svg-graph