Log Message:
py-networkx: updated to 2.2

2.2:
This release is the result of 8 months of work with over 149 commits by
58 contributors. Highlights include:
- Add support for Python 3.7. This is the last release to support Python 2.
- Uniform random number generator (RNG) handling which defaults to global
  RNGs but allows specification of a single RNG for all random numbers in NX.
- Improved GraphViews to ease subclassing and remove cyclic references
  which caused trouble with deepcopy and pickle.
- New Graph method `G.update(H)`