Sourcerank Semanantic Versioning for PyPi Changes

Sourcerank lists `MAJOR.MINOR.PATCH.post<x>` as an invalid semantic version, which it technically is, but when uploading to PyPi, you can't use dashes.

Trying to publish `MAJOR.MINOR.PATCH-post<x>` will switch it to `MAJOR.MINOR.PATCH.post<x>`. Sourcerank should count such versions as being valid semantic version numbers.