typos in convertrules.py

[Jean-Charles Malahieude via bug-lilypond]

I've noticed this while updating fr.po:


L 5476: UnisonoEvent, SoloOneEvent, and UnisonoEvent
  -> UnisonoEvent, SoloOneEvent, and SoloTwoEvent

L 5484: unisono-event, solo-one-event, and unisono-event
  -> unisono-event, solo-one-event, and solo-two-event

--
Jean-Charles