audit: complain about uppercase formula names

[scpeters]

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As recently discussed in #11440 (comment), our docs state that "Filenames should be all lowercase". This adds an audit to complain about formula names with uppercase letters and a test.

[BrewTestBot]

Review period will end on 2021-05-31 at 01:00:34 UTC.

[Rylan12]

I agree this audit makes sense, but I can't help but wonder whether the issue is really in Formulary's handling of this. I wonder if it should either downcase before initializing the formula or Formula#new should downcase the name before assigning.

[BrewTestBot]

Review period ended.

[MikeMcQuaid]

Makes sense to me! I agree with @Rylan12's comment but this PR is good to go as-is, I think.

brew/Library/Homebrew/github_packages.rb

Lines 134 to 136 in b6cfafe

	# TODO: consider changing the actual versions here and make an audit to
	# avoid these weird characters being used
	version_rebuild.gsub(/[+#~]/, ".")

This may be interesting to you, too. Would love a PR that also audits versions to match the format we want (so we don't have to hack around it like this).