deps: adds webrick as an explicit dependency for Ruby >=3

[mattxwang]

In Ruby 3, webrick (or WEBrick) is no longer packaged in to the default installation, and needs to be explicitly installed as a gem with bundle. This PR adds it, so that the build works as-intended for users on Ruby 3.

Note that this is a no-op on Ruby 2.

for more context, see: jekyll/jekyll#8523 and github/pages-gem#752

This is a precursor to my CI work for #92!

[mattxwang]

This also leads to another question, which is: should we standardize what Ruby version we use? Typically OSX/linux comes with ~ 2.6, though Ruby 3 supposedly has pretty large performance benefits! We could also include links to rvm and enforce a version with a .rvmrc or .ruby-lang!

[ctrueden]

should we standardize what Ruby version we use?

How does one go about doing that? Since most systems come with Ruby 2.6 or so, is there a downside to keeping compatibility with that version? You can still install Ruby 3 for the performance boost, no?

[mattxwang]

Thanks for the quick review! I'll start doing some CI work later tonight / earlier tomorrow.

How does one go about doing that?

To my understanding, we'd have to use something like rvm; not sure how many contributors this would affect (especially if they're on windows, where it's a bit arduous). If users have rvm, making an .rvmrc file auto-switches the user to the right ruby.

is there a downside to keeping compatibility with that version?

I don't think so necessarily, but I imagine eventually new gems will only support Ruby 3, in the same way that currently many node packages are shifting to pure ESM as Node v10 leaves LTS. Of course, if we lock users into Ruby 2, then we won't get the performance benefits from Ruby 3.

[adrienjoly]

The diff of this PR (found on github/pages-gem#752) helped me fixed a "Jekyll serve fails on Ruby 3.0 (webrick missing)" error when trying to serve my GitHub-pages site locally. Thank you!

[mattxwang]

The diff of this PR (found on github/pages-gem#752) helped me fixed a "Jekyll serve fails on Ruby 3.0 (webrick missing)" error when trying to serve my GitHub-pages site locally. Thank you!

Glad it was helpful! When I first encountered this problem last winter, it was definitely a headache resolving it!