In --require-hashes mode, all requirements must have their versions pinned with ==. These do not:
    python-dateutil!=2.0,>=1.0 from https://files.pythonhosted.org/packages/74/68/d87d9b36af36f44254a8d512cbfc48369103a3b9e474be9bdfe536abfc45/python_dateutil-2.7.5-py2.py3-none-any.whl#sha256=063df5763652e21de43de7d9e00ccf239f953a832941e37be541614732cdfc93 (from freezegun==0.3.11->-r tests.txt (line 39))
    requests>=2.0 from https://files.pythonhosted.org/packages/7d/e3/20f3d364d6c8e5d2353c72a67778eb189176f08e873c9900e10c0287b84b/requests-2.21.0-py2.py3-none-any.whl#sha256=7bf2a778576d825600030a110f3c0e3e8edc51dfaafe1c146e39a2027784957b (from responses==0.10.4->-r tests.txt (line 44))