Use more exact regex for Bitbucket strategy.

[reitermarkus]

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Previously, this also wrongfully matched https://bitbucket.org/blackosx/darwindumper/wiki/DD_AppCast.xml.

Extracted from #9529.

[BrewTestBot]

Review period will end on 2020-12-22 at 00:00:00 UTC.

[samford]

We've already reviewed and discussed this as part of #9529 and I'm good with this approach. I'll update the other strategies to bring them in line with this refactoring after I've reviewed (and either merged or closed) #9519.

For what it's worth, bathyscaphe also runs into an undefined method sub!' for nil:NilClasserror in relation to thesuffix.sub!(/.t(?:ar..+|[a-z0-9]+)$/i, ".t")call, assuffixisnil` in this case. This PR addresses this issue as well.

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I pushed a commit to bring URL_MATCH_REGEX in line with the more explicit regexes we're using in #9519. Namely, I added the protocol as an anchor at the start of the regex (https?://). [I also modified the regex to have the forward slashes at the start of lines, to align the style with multiline regexes in some other strategies.]

As part of reviewing #9519, I'm working on bringing the other strategies in line with the Bitbucket approach here.

[BrewTestBot]

Review period ended.