Disable Heroku test-package stage

Travis builds are timing out due to [timeout limits](https://docs.travis-ci.com/user/customizing-the-build/#build-timeouts)
Disable tests against Heroku until we can speed them up, parallelise them, or split them into separate jobs.

.travis.yml

@@ -20,7 +20,7 @@ before_deploy:
  - openssl aes-256-cbc -K $encrypted_5e88d222d606_key -iv $encrypted_5e88d222d606_iv -in .heroku-netrc.enc -out .heroku-netrc -d
  - cat .heroku-netrc >> $HOME/.netrc
  - cf login -a $CF_ENDPOINT -u $CF_USERNAME -p $CF_PASSWORD
- - ./test-package.sh --skip-package
+ - ./test-package.sh --skip-package --skip-heroku
  - docker run -v $TRAVIS_BUILD_DIR/deployment/helm/:/helm -w /helm --entrypoint /helm/build.sh alpine/helm:3.0.0-beta.5 $TRAVIS_TAG
 
 deploy: