travis: run gulp protractor

[gruppjo]

As discussed here: #478 I gave protractor another run as part of our Continuous Integration setup with travis. This could ensure the functionality of the default protractor setup and tests with every build.

Unfortunately I couldn't get it to run (see this build: https://travis-ci.org/mwaylabs/generator-m-ionic-demo/builds/201915053).

This issue over at the travis repo is worth looking into: travis-ci/travis-ci#272

It's also possible that our test are not written properly. It might be worth to reduce the tests to a minimum viable case to see if the setup is the problem or the tests we generate.

[gruppjo]

Another setup with (sudo apt-get install chromium-chromedriver): travis-ci/travis-ci#272 (comment)

Still no success, reverting: https://travis-ci.org/mwaylabs/generator-m-ionic-demo/jobs/211345005