Merge branch 'rs-update-sprockets' into 'master'

Bump sprockets to 3.7.2 to address CVE-2018-3760

See merge request gitlab-org/gitlab-ce!20109

Gemfile.lock

@@ -867,7 +867,7 @@ GEM
       activesupport (>= 4.2)
     spring-commands-rspec (1.0.4)
       spring (>= 0.9.1)
-    sprockets (3.7.1)
+    sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-rails (3.2.1)