Fix rhyming_part docstring
Fix rhyming_part docstring

`phones_for_word("purple")` returns a list: `[u'P ER1 P AH0 L']`
`rhyming_part` expects a string parameter, e.g. `'P ER1 P AH0 L'`
hugovk/pronouncingpy,aparrish/pronouncingpy