Merge branch 'bump-gitpython' into 'master'

Bump Python requirement gitpython to 3.1.9

See merge request !978

requirements.txt

@@ -13,7 +13,7 @@ django-enumfields==2.0.0
 django-redis==4.12.1
 djangorestframework==3.11.1
 elasticsearch-dsl>=6.0.0,<7.0.0
-gitpython==3.0.8
+gitpython==3.1.9
 python-gitlab==1.7.0
 python-memcached==1.59
 pytz==2020.1