Upgrade Flow and Babel dependencies

[Jack-Barry]

What's the problem this PR addresses?

I forget where I saw it, but remember reading that a shift over to TypeScript from Flow would be welcome here. I decided to go ahead and upgrade Babel so that the transition will be more feasible.

• This fixes at least part of Upgrade dependencies #47 by upgrading Babel dependencies
• This upgrades the Flow dependency so that plugin for VS Code can be used until the shift over to TypeScript is complete

How did you fix it?

Upgraded dependencies and fixed any places that the upgrades broke tests.

[Jack-Barry]

Taking another look at this on a PC at work - everything was passing on my Mac at home - might be the Node version I was using (12.13.1, will try it again in 10.17.0 and 8.16.2).

[Jack-Barry]

Attempting a change in the test fixture - passes on my WSL under 10.17.0, but the erroring test is skipped on Windows OS.

[Jack-Barry]

🤷🏻‍♂️ No idea what's going on here. I think it's probably a race condition somewhere given that it's passing in all environments except Node 10 with WEBPACK_VERSION=4 MOCHA_VERSION=5.

Doesn't make much sense that it would pass in Node 10 on Mocha 4 and 6 but not 5 since it's in between those so any breaking changes would be affecting 6. Maybe the timeout on those failing specs needs to be bumped up a bit to 30000?

[Klitsenko]

@Jack-Barry These cli --watch tests are unreliable (they fail for me all the time since I forked mocha-webpack), I'm not sure why are them there indeed. I'm fine with disabling them for now. If you are brave you can figure out how to make them more reliable.

[Jack-Barry]

I'm brave but not feeling that brave right now 😐 haha. Reworked the file to use xdescribe instead of commenting out specs so that at least the tests are visible as skipped when being run.

[Klitsenko]

@Jack-Barry Very nice, thank you!

[larixer]

Cool, looks great, many thanks!