Fail travis build if db/schema.rb is missing commit of update

MSP-11616

Use `git diff --exit-code` to exit with 1 and fail the build if there is
an update to db/schema.rb after `rake db:migrate` runs on travis.

Author: limhoff-r7

.travis.yml

@@ -20,6 +20,8 @@ before_script:
   - bundle exec rake --version
   - bundle exec rake db:create
   - bundle exec rake db:migrate
+  # fail build if db/schema.rb update is not committed
+  - git diff --exit-code
 script: "bundle exec rake $RAKE_TASK"
 
 rvm: