Mark as invalid sentences with digits

[kdavis-mozilla]

As texts with digits, e.g. "Room 456", can be read in many valid ways, e.g. "Room four five six" or "Room four hundred fifty six", cleaning the text requires listening to all the associated audio.

Unfortunately, the amount of audio which this implies to be listened to is too great to be listened to before the impending release. Thus, sentences with digits should be marked as invalid as a precautionary precaution against pollution of the data set.