Pass a string URI to Launchy.open in DeliveryMethod#deliver!

The version of Launchy I am using (2.3.0) in a
Rails 2.3.5 project is not happy with what
`Uri.parse` returns for OS X paths (which is
an instance of `URI::Generic`). Thus nothing
opens.

However, when I pass it string path/uri, it
seems to work fine.
Merge pull request #1 from mitio/patch-1

Pass a string URI to Launchy.open in DeliveryMethod#deliver!