Fix warnings in tests

[notexactlyawe]

The test suite produces a lot of warnings, for example, see the below when running test_create_game.py:

================================================================================================ warnings summary =================================================================================================
venv/lib/python3.6/site-packages/dns/hash.py:25
  /home/cameron/src/negativei2-server/venv/lib/python3.6/site-packages/dns/hash.py:25: DeprecationWarning: dns.hash module will be removed in future versions. Please use hashlib instead.
    DeprecationWarning)

test/routes/test_create_game.py::CreateGameTest::test_controller_id_not_exist
test/routes/test_create_game.py::CreateGameTest::test_controller_offline
test/routes/test_create_game.py::CreateGameTest::test_create_game_object_sensible
test/routes/test_create_game.py::CreateGameTest::test_create_then_get_game
test/routes/test_create_game.py::CreateGameTest::test_invalid_creator_id
test/routes/test_create_game.py::CreateGameTest::test_invalid_player_id
test/routes/test_create_game.py::CreateGameTest::test_negative_time_per_player
  /home/cameron/src/negativei2-server/venv/lib/python3.6/site-packages/marshmallow/schema.py:364: ChangedInMarshmallow3Warning: strict=False is not recommended. In marshmallow 3.0, schemas will always be strict. See https://marshmallow.readthedocs.io/en/latest/upgrading.html#schemas-are-always-strict
    ChangedInMarshmallow3Warning

-- Docs: https://docs.pytest.org/en/latest/warnings.html
====================================================================================== 7 passed, 8 warnings in 0.64 seconds =======================================================================================

This issue can be closed when there are no warnings in the test suite.