[Code Style] Run checkstyle on CircleCI

Run the full gulp verify task for testing on CircleCI, to handle
unit tests as well as code style checks and linting (and other
verification steps that may be added in the future.)

circle.yml

@@ -15,8 +15,8 @@ deployment:
     heroku:
       appname: openmctweb-staging-deux
 test:
-  post:
-    - gulp lint
+  override:
+    - gulp verify
 
 general:
   branches: