Replace dashes with dots for gem version

When switching out to using git-describe for versioning from
source, gem versioning breaks because dashes are not allowed.
This simple fix replaces the dashes with dots, which are.
Note that in a merge-up to 3.0.x, this commit will conflict.
Default to 'ours' in a merge-up, this file does not even exist
in 3.0.x and shouldn't.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>