Fix to missing self._vowels

Merge pull request #24 from linuxgoose/23-caverphone-2-__vowels-undefined-error

23 caverphone 2   vowels undefined error

Update caverphone2.py

Merge pull request #22 from linuxgoose/10-add-caverphone1-and-caverphone2

10 add caverphone1 and caverphone2

Implementation of Caverphone 2 algorithm