formula_auditor: audit redis relicense

[p-linnane]

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Redis has made the unfortunate decision to relicense under a non-OSI license. This PR sets up an audit to prevent Redis from being updated to the relicensed version.

[apainintheneck]

Would it make more sense to generalize the logic here so that it's not specific to redis? We already do something similar when auditing Hashicorp formulae so maybe they can be combined into a more generic audit_relicensed_formulae check.

[p-linnane]

I considered it, but opted for just getting it added. There's also one for Elasticsearch/Kibana though...so maybe it's about time.

[apainintheneck]

Yeah, I think it's time. It shouldn't be that difficult. Just remove hashicorp from the names of methods and constants and add the new formula-version pair to the hash.

Also, could you fix this typo while you're in this file?

brew/Library/Homebrew/formula_auditor.rb

Line 508 in 7b2bfee

"vagrant-compleion" => "2.4",

[apainintheneck]

Thanks for cleaning up the audit!

[MikeMcQuaid]

Great work, thanks for the PR @p-linnane and for the nice suggestion @apainintheneck!