Add audit for livecheck in casks.

[reitermarkus]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
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• Have you successfully run brew man locally and committed any changes?

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Check if casks with livecheck blocks have a version and if that version is the same as returned by the livecheck.

[BrewTestBot]

Review period will end on 2020-12-15 at 14:24:52 UTC.

[BrewTestBot]

Review period ended.