Update rasa/core/channels/facebook.py
Update rasa/core/channels/facebook.py

Co-Authored-By: Tom Bocklisch <96835dd8bfa718bd6447ccc87af89ae1675daeca@rasa.com>
RasaHQ/rasa_nlu,RasaHQ/rasa_nlu,RasaHQ/rasa_nlu