Update sprockets-rails to version 3.1.1

Author: sferik

Gemfile.lock

@@ -187,7 +187,7 @@ GEM
     sprockets (3.6.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
-    sprockets-rails (3.0.4)
+    sprockets-rails (3.1.1)
       actionpack (>= 4.0)
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)