Update h5py to 2.3.1

Building h5py <= 2.3.0 fails with the latest hdf5 (1.8.13).
This was fixed in h5py 2.3.1, see [1].

[1] https://github.com/h5py/h5py/issues/446
Merge pull request #781 from fzadow/new-h5py-version

Update h5py to 2.3.1 in pip-frozen