Ignore version checking if building latest tag.

[bmaher]

Part of #6.

Description

This PR fixes a bug where Travis CI builds tags after merges to master, resulting in a failure in the version checking script (versions matched between master and tag).

Instructed Travis to ignore all branches matching a regex representing tags /^v\d+\.\d+(\.\d+)?(-\S*)?$/.

Types of Changes

What types of changes does your code introduce? Keep the ones that apply:

• Configuration change

Review

Reviewers' checklist:

• If this PR implements new flows or changes existing ones, are there
  good tests for these flows?
  If this PR rather removes flows, are the obsolete tests removed as well?
• Is the documentation still up-to-date and exhaustive? This covers both
  technical (in source files) and functional (under docs/) documentation.
• Is the changelog updated?
• Does the new version number correspond to the actual changes from this PR?
  In doubt, refer to https://semver.org.

After this PR

Any follow-up action necessary?

[zincr]

🤖 zincr found 0 problems , 0 warnings

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[tortila]

I wonder if there's an easier solution to this problem - perhaps we could just skip builds from tags? I found this feature of Travis: https://docs.travis-ci.com/user/customizing-the-build/#safelisting-or-blocklisting-branches that explains this exact use case. What do you think @bmaher @thilp?