Pin hypothesis at 4.2.3 (#283)
Pin hypothesis at 4.2.3 (#283)

https://travis-ci.org/django/daphne/jobs/595912612

Requirement already satisfied: attrs>=17.4.0 in /home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages (from twisted) (18.2.0)

hypothesis 4.40.0 has requirement attrs>=19.2.0, but you'll have attrs 18.2.0 which is incompatible.
django/daphne