Update __init__.py

user_playlist doesn't work with starred playlists, which pass an ID of None.

This will allow the user to pull data for starred playlists, which use the URI users/%s/starrred

spotipy/__init__.py

@@ -206,6 +206,8 @@ class Spotify(object):
     def user_playlist(self, user, playlist_id, fields=None):
         ''' Gets playlist of a user
         '''
+        if playlist_id == None:
+            return self.get("users/%s/starred" % (user), fields=fields)
         return self.get("users/%s/playlists/%s" % (user, playlist_id), fields=fields)
 
     def user_playlist_create(self, user, name, public=True):