Hypothesis-networkx

Update the requirements to allow the use of Networkx 3 and higher.

What's Changed
* Update to networkx 3 by pckroon in https://github.com/pckroon/hypothesis-networkx/pull/18


**Full Changelog**: https://github.com/pckroon/hypothesis-networkx/compare/v0.2.2...v0.3.0

This release fixes an edge case where using a multigraph with `max_edges=None` would raise a TypeError. Many thanks to gmacon for finding and fixing this!

Added the Hypothesis trove classifier.

Still the same code as v0.1.0, but let's see if I can make Travis deploy it to PyPI