fix requirements.txt dep + >80 column python file
requirements.txt: s/dateutil/python-dateutil/
Test Plan
pip install -r requirements.txt
Migrated from D118 (view on Phabricator)
Staging instance, all changes can be removed at any time
requirements.txt: s/dateutil/python-dateutil/
pip install -r requirements.txt
Migrated from D118 (view on Phabricator)