python3: CPython has migrated to GitHub

[yan12125]

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

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CPython has migrated to GitHub. [1][2] The old mercurial repository [3] is no longer updated.

Since Homebrew/brew#1844, brew audit --strict returns an error:

$ brew audit --strict python3
==> Installing or updating 'rubocop' gem
Fetching: rubocop-0.47.1.gem (100%)
Successfully installed rubocop-0.47.1
1 gem installed
python3:
  * macOS has been 64-bit only since 10.6 so universal options are deprecated.
Error: 1 problem in 1 formula

Should I handle it in this PR, too?

[1] https://github.com/python/cpython/
[2] https://mail.python.org/pipermail/python-dev/2017-February/147381.html
[3] https://hg.python.org/cpython/

[yan12125]

Error Message

failed: brew linkage --test fdroidserver

Stacktrace

        Missing libraries:
  /usr/local/opt/little-cms2/lib/liblcms2.2.dylib

Just like #7654, fdroidserver breaks tests...

[JCount]

I am not certain about the universal question, but I can say that fdroidserver's breakage is not at all related to this PR and you can safely just ignore it at this point. (as you probably already guessed)

[MikeMcQuaid]

Thanks for your contribution to Homebrew! Without people like you submitting PRs we couldn't run this project. You rock!