Merge pull request #1061 from broadinstitute/jb-sprockets-rollback

Reverting to sprockets 3.7.2 re: segfault errors on ubuntu (SCP-3387)

Author: bistline

Gemfile.lock

@@ -457,7 +457,7 @@ GEM
     simplecov-html (0.12.3)
     simplecov-lcov (0.8.0)
     simplecov_json_formatter (0.1.3)
-    sprockets (4.0.2)
+    sprockets (3.7.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-rails (3.2.2)