Fix day is out of range for month

[freenerd]

day is out of range for month
Traceback (most recent call last):
File "/base/python_lib/versions/1/google/appengine/ext/webapp/init.py", line 509, in call
handler.post(*groups)
File "/base/data/home/apps/tracksonamap/1.337270160096570688/backend_update_track.py", line 153, in post
backend_utils.write_track_to_datastore(track, user, location)
File "/base/data/home/apps/tracksonamap/1.337270160096570688/backend_utils.py", line 123, in write_track_to_datastore
release_date = datetime.date(year=int(track['release_year'] or 1900), month=int(track['release_month'] or 1), day=int(track['release_day'] or 1))
ValueError: day is out of range for month