Fix own UserWarning in test suite
Fix own UserWarning in test suite

The following message was printed to stderr:
tests/test_using.py:2516: UserWarning: Setting a specific random seed
for FuzzyDate can still have varying results unless you also set a
specific end date. For details and potential solutions see
https://github.com/FactoryBoy/factory_boy/issues/331

FactoryBoy/factory_boy,rbarrois/factory_boy