[WIP] Add Travis CI configuration.

[MikeMcQuaid]

Just testing Travis for our main PRs.

[xu-cheng]

Travis CI has its own copy of Homebrew. And I think it would be best if we can run test on the clone copy. At the other hand, we need to test formula with prefix of /user/local. Therefore, can or should we do something like this:

rm /usr/local/bin/brew
ln -sf $PWD/bin/brew /usr/local/bin/brew
mkdir -p /usr/local/Cellar

[MikeMcQuaid]

@xu-cheng Yep, need to work that out. I'm wondering if there's a way to coax Travis into checking out into a certain directory.

[xu-cheng]

Another thing I just found is Travis CI supports custom log folding. We can use it to fold log inside brew test-bot. Refs:

• Log folding for selected commands travis-ci/travis-ci#2285 (comment)
• https://github.com/macbre/travis-fold

[MikeMcQuaid]

@xu-cheng Great idea.

[xu-cheng]

This should be just:

rvm: 
   - system

[MikeMcQuaid]

Yep.

[MikeMcQuaid]

@xu-cheng Looks like this is green now. Thoughts on merging?

[xu-cheng]

A style nit, I would prefer if else then if return.

[MikeMcQuaid]

I prefer early return 😉

[xu-cheng]

I usually use early return in nested or complex conditions. To me, using it in simple binary conditions makes the code imbalance or asymmetric. Anyway, your call.