Merge 2.2.x after 2.2.0-M3 release

[travisbrown]

I went ahead and removed the Scala.js cross-publishing script, but we can always recover it from the history if we need to publish for 0.6 again.

Please note that this needs to be a merge commit! If we squash or rebase, then the 2.2.0-M3 tag won't be on master.

[codecov-commenter]

Codecov Report

Merging #3475 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3475   +/-   ##
=======================================
  Coverage   91.77%   91.77%           
=======================================
  Files         383      383           
  Lines        8394     8394           
  Branches      212      204    -8     
=======================================
  Hits         7704     7704           
  Misses        690      690           

[barambani]

🎉

[travisbrown]

@LukaJCB This definitely isn't a big deal, but we'll need the 2.2.x branch for at least the next couple of releases. I've just been following PROCESS.md on this: merge master into 2.2.x, push and publish from there, and then PR 2.2.x back onto master. There's no reason I guess that 2.2.x has to stay on GitHub in the meantime, but I think it makes things a little clearer.

[LukaJCB]

oh sorry, I must've done that completely subconsciously, I don't even remember doing it.