Setting up Travis to auto deploy docs to gh-pages

Now that @hakilebara did all the hard work in getting us on ember-cli-addon-docs (thanks again!), we can now hook it up to our Travis CI pipeline to auto publish.

Open questions/comments

• Will this change how we publish versions?
• We can remove /docs and update any links/sourcecode references pointing to those docs.
• Will we be able to default to the latest version and avoid linking directly to /versions/master
  • I suspect the need to provide a version goes away once we start deploying tagged releases
• Disable https://github.com/ember-intl/ember-intl.github.io?
  • I have no idea how these deploys are occurring cc @Turbo87

[jasonmit]

This should now be all squared away. Thanks again for all your hard work @hakilebara!

[jasonmit]

It’s all working locally, just need to fix the deploy stage in CI:

No deployKeyordeployKeyPath configured