[tictactoe] Fix replying to request

tictactoe/manifest.ini

 [info]
 name: Tic tac toe
 short_name: Tic tac toe
-version: 0.2.2
+version: 0.2.3
 description: Play tic tac toe
 authors = Yann Leboulanger <asterix@lagaule.org>
 homepage = http://trac-plugins.gajim.org/wiki/TictactoePlugin

tictactoe/plugin.py

@@ -288,7 +288,7 @@ class TicTacToeSession(stanza_session.StanzaSession):
         game = invite.getTag('game')
         x = game.getTag('x', namespace='jabber:x:data')
 
-        form = xmpp.DataForm(node=x)
+        form = xmpp.DataForm(node=str(x))
 
         if form.getField('role'):
             self.role_o = form.getField('role').getValues()[0]