Fix and Improve WASM CI

[josephlr]

Fixes #113

• Always use latest Firefox
  • We have to use latest Chrome, so we might as well do the same thing here.
• Explicitly pin wasmtime and cargo-web
  • We don't need a particular version here, so we might as well pin to avoid CI breakage.
• Make sure our wasm-bindgen-test-runner and wasm-bindgen versions match
  • This uses the cargo metadata command (which is an awesome thing I just learned about).

We now consistently use the $VERSION environment variable to make our intentions explicit (and to avoid repeating version numbers).

[josephlr]

Hey @newpavlov @dhardy I still have Write access to this repo, but I wasn't able to merge this PR ("You’re not authorized to merge this pull request.") even though it was approved. Is this intentional, or did something change? I was able to merge #108 just fine a few days ago.

For the Google repos I maintain, I set the branch protection rules to be:

• master is protected, so no force pushing
• All PRs against master require approval
• PRs require approval from at least one other user with Write permission
• Once approved, anyone with Write access can merge the PR

I thought that's what getrandom had as well, but it seems like that's not the case.

[dhardy]

Sorry @josephlr, that was me; I demoted you from "Maintain" to Write access; according to the description this should still let you manage PRs so I don't know why this happened.

I checked the branch protection (merge review, push, and now status checks); these shouldn't be an issue. Hmm, I'll bump you back to Maintain then (according to the description the only difference is some repo settings).

[josephlr]

Sorry @josephlr, that was me; I demoted you from "Maintain" to Write access; according to the description this should still let you manage PRs so I don't know why this happened.

That's really weird, I agree that the docs suggest I should only need Write permission to merge approved PRs. It might be a bug in Github's new permissions settings, or just some unclear docs. I haven't dealt that much with Triage/Maintain permissions as the new permissions Beta hasn't rolled out to the Google org yet.