Merge pull request #573 from Shopify/dependabot/bundler/dev/mocha-2.7.1

Bump mocha from 2.3.0 to 2.7.1 in /dev

Author: tylerrowsell

dev/Gemfile.lock

@@ -104,7 +104,7 @@ GEM
     minitest (5.25.1)
     minitest-hooks (1.5.2)
       minitest (> 5.3)
-    mocha (2.3.0)
+    mocha (2.7.1)
       ruby2_keywords (>= 0.0.5)
     parallel (1.26.3)
     parser (3.3.6.0)