BUG: common.is_hashable returns False for np.float64 on Python 3

[shoyer]

xref #8929
xref #9193

Here are some test results on Travis-CI illustrating the issue and my commit

Any ideas for the fix? This is quite likely a numpy bug, but it's one we need to work around. The simplest thing would be revert back to just calling hash, but I expect that would cause some other test cases to fail.

CC @aevri