Update requirements.txt

Author: jonomon

source/notebooks/requirements.txt

@@ -131,7 +131,7 @@ python-dateutil==2.8.1
     #   pandas
 pytz==2020.4
     # via pandas
-pyyaml==5.3.1
+pyyaml==5.4
     # via
     #   awscli
     #   papermill