Remove trailing commas in metadata.json

The commas after operatingsystem compatiblity expressions created
invalid JSON that could not be properly built into a release tarball.
This commit removes each. A future commit could remove all but
operatingsystem_support from the root metadata.json and the result
of puppet module build would still produce the right metadata.
Merge pull request #47 from ryanycoleman/metadata_fix

Remove trailing commas in metadata.json