Fix linting dependencies
-r pip.txt
# prospector 1.1.6.2 is not compatible with 2.1.0
-astroid<2.1.0
+astroid<=2.0.4
# prospector 1.1.6.2 is not compatible with 2.2.2
-pylint<2.2.2
+pylint<=2.1.1
pylint-django<2.0.5
pylint-celery==0.3
prospector==1.1.6.2
