Docs: Update https://material.angularjs.org to pull from tag instead of master branch

[marcysutton]

To minimize breakage of the docs site ahead of the version picker (#918), the Angular Material core team discussed publishing code to https://material.angularjs.org from a tag rather than the master branch. That way, breaking code inadvertently pushed to master will not affect the docs site. Developers can continue to build the docs locally from any branch, tag, or commit–only the live docs site will be published from specific tag.

Ideally, we would also run tests in our deployment process to ensure breaking code is not pushed to the live site.

[marcysutton]

@ajoslin is this done now?

[marcysutton]

@ajoslin @rschmukler let's keep talking about this one.

[ThomasBurleson]

This will not be needed when we publish the Documentation with a version picker and snapshots on a CDN each document build.