docs: update chat/support links

[shellscape]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

We've moved chat to Discord and are closing down the Gitter. This updates all of the links in this repo.

[rollup-bot]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#docs/discord

or load it into the REPL:
https://rollupjs.org/repl/?circleci=13449

[codecov]

Codecov Report

Merging #3861 (68f91b6) into master (fd809d5) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3861      +/-   ##
==========================================
- Coverage   97.07%   97.06%   -0.01%     
==========================================
  Files         184      184              
  Lines        6523     6517       -6     
  Branches     1889     1887       -2     
==========================================
- Hits         6332     6326       -6     
  Misses        101      101              
  Partials       90       90              

Impacted Files	Coverage Δ
src/ast/nodes/TryStatement.ts	94.11% <0.00%> (-1.54%)	⬇️

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[Rich-Harris]

What's the rationale for using a URL shortener? Seems like an unnecessary point of failure

[shellscape]

A friendlier presentation, ease of sharing from memory without looking it up. Discord currently lacks a friendly invite url.

[Rich-Harris]

Fair enough. Ideally it'd be https://rollupjs.org/chat, like we have with https://svelte.dev/chat, but that's tricky with a statically exported site (it'd work, sort of, because it just creates a page with <script>location.href = 'blah'</script> but that's not ideal). Maybe that'd make sense once we release SvelteKit and it's possible to make /chat a serverless function that redirects while everything else is static

[shellscape]

Could we just use a meta redirect? I'm not familiar with how the docs site is built, but I could look into it.

[Rich-Harris]

Oh shit, I had no idea such a thing existed. Yeah, if we added a /chat/index.html file to https://github.com/rollup/rollupjs.org/tree/master/static containing

<meta http-equiv="refresh" content="0;url=http://discord.com/whatever"

then it should Just Work?