google-calendar: Update requirements.txt dependencies.

Author: Niloth-p

zulip/integrations/google/google-calendar

@@ -1,7 +1,4 @@
 #!/usr/bin/env python3
-#
-# This script depends on python-dateutil and python-pytz for properly handling
-# times and time zones of calendar events.
 import argparse
 import datetime
 import itertools

zulip/integrations/google/requirements.txt

@@ -1,2 +1,4 @@
 httplib2>=0.22.0
 oauth2client>=4.1.3
+python-dateutil
+pytz