Remove fast_finish in travis.yml.

[jdalton]

I noticed a fast_finish entry in the travis.yml.
I hadn't seen that option before and looked it up.

It seems to only apply if you allow_failures which I don't see in the yml.

[zpao]

Thanks! That was there because we used to allow some of those pesky in-browser tests to fail and I missed this option when removing them in your favorite PR :P (https://github.com/facebook/react/pull/4393/files#diff-354f30a63fb0907d4ad57269548329e3)

[jdalton]

FWIW I've been able to get pretty stable tests using saucelabs for nearly 2 years now.
The thing that made it work, which can be applied to any remote testing setup/service, is adding in levels of retries. From retrying the async test in QUnit, to retrying a faulty test run from sauce, to retrying the sauce tunnel connection. With those in place, I hardly ever have false fails.

[zpao]

I remember seeing something about that a while ago, so thanks for the reminder. We'll keep that in mind and probably crib from lodash whenever #5703 gets done.