Upgrade to the latest react and react-dom

[smashwilson]

Now that atom/electron-link#15 is out, we should be able to update to the latest React builds without hitting weird snapshotting errors or silently falling back to ancient browser shims.

Fixes #1832.

[codecov]

Codecov Report

Merging #1884 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1884      +/-   ##
==========================================
+ Coverage   91.22%   91.24%   +0.01%     
==========================================
  Files         196      196              
  Lines       10745    10745              
  Branches     1574     1574              
==========================================
+ Hits         9802     9804       +2     
+ Misses        943      941       -2

Impacted Files	Coverage Δ
lib/atom/decoration.js	85.54% <0%> (+1.2%)	⬆️
lib/atom/gutter.js	92.3% <0%> (+2.56%)	⬆️

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[smashwilson]

Oh, right, this probably needs #1885.

[annthurium]

do we need to do any manual testing? Or are you pretty confident that the newest versions of these libs aren't gonna break anything??

also, is this the version with hooks??

[smashwilson]

do we need to do any manual testing? Or are you pretty confident that the newest versions of these libs aren't gonna break anything??

For React, yeah, I was going to at least take it for a spin and make sure it runs. Our tests should catch anything that regressed, but just to be sure.

also, is this the version with hooks??

lol

[smashwilson]

I fired it up and clicking around a bit and it looks like we're still good 👌

[annthurium]

cool, let's ship it! Thanks for doing the manual testing.