Fix version bump 

Etsy uses "vX.Y.Z" rather than "X.Y.Z" when tagging releases.
Otherwise git gives an error: Unable to parse SHA reference for '0.7.0' in repository 'git://github.com/etsy/statsd.git'. Verify your (case-sensitive) repository URL and revision.
Merge pull request #11 from willoller/patch-1

Fix version bump