update gemfiles for travis

Author: rmosolgo

.travis.yml

@@ -21,7 +21,7 @@ gemfile:
   - gemfiles/rails_4.2_sprockets_2.gemfile
   - gemfiles/rails_4.2_sprockets_3.gemfile
   - gemfiles/rails_5_no_sprockets.gemfile
-  - gemfiles/rails_5_sprockets_4.gemfile
+  - gemfiles/rails_5.1_sprockets_4.gemfile
 
 matrix:
   fast_finish: true
@@ -43,7 +43,7 @@ matrix:
     - rvm: 2.1
       gemfile: gemfiles/rails_5_no_sprockets.gemfile
     - rvm: 2.1
-      gemfile: gemfiles/rails_5_sprockets_4.gemfile
+      gemfile: gemfiles/rails_5.1_sprockets_4.gemfile
     - rvm: jruby-9.0.1.0
       gemfile: gemfiles/rails_4.0.gemfile
     - rvm: jruby-9.0.1.0