* Update all Jest packages to 17.x, cache babel-jest transforms
* Remove the caching
Looking at the other builds it doesn't seem to actually be that necessary. The bottleneck is executors, not build time.
* Remove unnecessary package, fix fiber test runner
* Regenerate yarn lockfile
* Update ESLint to 3.10.2
Also pull in fbjs for extending properly, per @zpao. This also disables consistent-return, which has about 80 failing cases in React currently. If we'd like to turn this back on, we should do it separately and fix all the call sites properly (rather than just adding 'return undefined;' everywhere, which adds no value.
Fixes to all existing lint errors plus an update for yarn.lock to follow.
* Update yarn.lock after the eslint update.
* Fix all new eslint failures
Unfortunately I had to add three eslint-disable-next-line instances. All have explanations inline.
* Switch Travis to use yarn instead of npm
I couldn't figure out how to do this yarn alone so I ended up
just manually hacking the yarn to force a downgrade of babylon
to 6.8.0 since otherwise it gets resolved to 6.12.0 which is
broken.