TST: build against numpy 1.9.3 instead of 1.8.1 on Appveyor; use Cython 0.23.4
TST: build against numpy 1.9.3 instead of 1.8.1 on Appveyor; use Cython 0.23.4

Reason for change: there is no 1.8.1 wheel for Python 3.5 on the
Rackspace host.  And anyway this is not a bad change.

Same for Cython: PyPi now has Windows wheels for 0.23.4, while the 0.20.2
wheel for Python 3.5 was missing on Rackspace.

michelp/pywt,eriol/pywt,michelp/pywt,PyWavelets/pywt,PyWavelets/pywt,eriol/pywt,michelp/pywt,rgommers/pywt,kwohlfahrt/pywt,kwohlfahrt/pywt,rgommers/pywt,grlee77/pywt,rgommers/pywt,rgommers/pywt,kwohlfahrt/pywt,grlee77/pywt,eriol/pywt