Force git to return something if tags aren't found

If there are no tags in the current repository, this command will fail leaving the OSQUERY_BUILD_VERSION blank, and therefore breaking the package building process (and presumably other things too) due to the empty version flag.  By adding the flag --always, this forces git to fallback to a commit id instead of returning nothing.
Merge pull request #532 from arirubinstein/master

Force git to return something if tags aren't found