Allow hyphens in arc library names
Allow hyphens in arc library names

Summary:
We've had these in our library names and they're quite useful as word
separators. Allowing them shouldn't cause any trouble.

Test Plan:
ran arc liberate in an empty directory, and it didn't complain when I gave
it a name with a hyphen.

Reviewers: epriestley, vrana, jungejason

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3070

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