Switch to mainline cache_digests gem

lrbalt's 1.8.7-compatible fork is no longer necessary to use.

Gemfile

@@ -17,7 +17,7 @@ gem "aasm"
 gem "htmlentities"
 gem "swf_fu"
 gem "rails_autolink"
-gem "cache_digests", :git => 'git://github.com/lrbalt/cache_digests.git'
+gem "cache_digests"
 gem "rack-mini-profiler"
 
 # Gems used only for assets and not required

Gemfile.lock

@@ -1,10 +1,3 @@
-GIT
-  remote: git://github.com/lrbalt/cache_digests.git
-  revision: 8469c4153c84c0d918b01daccaa1e69747e93e89
-  specs:
-    cache_digests (0.1.0)
-      actionpack (>= 3.2)
-
 GEM
   remote: https://rubygems.org/
   specs:
@@ -49,6 +42,8 @@ GEM
     builder (3.0.4)
     bullet (4.3.0)
       uniform_notifier
+    cache_digests (0.2.0)
+      actionpack (>= 3.2)
     capybara (2.0.2)
       mime-types (>= 1.16)
       nokogiri (>= 1.3.3)
@@ -209,7 +204,7 @@ DEPENDENCIES
   aruba
   bcrypt-ruby
   bullet
-  cache_digests!
+  cache_digests
   capybara
   coffee-rails
   cucumber-rails