Stop distribute script from uploading builds on new branch and tag

[brockboland]

Our distribute.sh script checks if the build is running for a pull request and bails out if so, but it will continue on builds for new branches or tags (as well as merge builds, but that's the intended behavior).

This script should handle things differently in these cases, though I'm debating how differently. Distributing builds to HockeyApp and/or TestFlight for new branches and tags might be OK, but the release notes added to those should at least indicate which branch or tag the build is for (which can be accomplished using environment vars: https://docs.travis-ci.com/user/environment-variables/). Hockey builds include release notes (which currently indicate whether it's a staging or prod build). The pilot tool has a "changlog" option that's used for iTunes Connect builds, but I can't figure out if that's actually displayed anywhere in iTunes Connect.

Relevant environment variables:

• TRAVIS_TAG
• TRAVIS_BRANCH

[vokal-isaac]

n.b., it's possible to specify regex(es) for branches/tags to not build in .travis.yml, which we use to keep Travis from building the tags automatically generated by uploaded builds (https://github.com/vokal/Xcode-Template/blob/master/Vokal-Cocoa%20Touch%20Application%20Base.xctemplate/.travis.yml#L42-L44). I think it's also possible to specify only the tags/branches to include, rather than excluding some, and that we'd made the intentional decision that any tags/branches in the company shared repo should get built.

[brockboland]

Letting Travis build for tags and branches is fine, I just don't think it should be distributing builds for these.