Please report any errors to the issue tracker.
If you can submit a fix for a bug, then please fork the repository, and issue a pull request once done.
If the bug concerns the pattern matching or the replacing (text not replaced as it should be, or text that should not replaced is) always submit a test to validate your fix against.
If it's not a bug and the fix is trivial, having a test is not an absolute necessity but you gets (lots of) bonus points.
The process is basically the same as for bug fixes. If you provide code that does what you'd like to see in the gem, please issue a pull request. If you propose a feature, open a ticket.