change install_requires order to fix scipy install on readthedocs
change install_requires order to fix scipy install on readthedocs

Building docs on readthedocs.org requires dependencies to be installed. "pip
install scipy" fails if numpy is not there already and for whatever reason, pip
installs the last dependency first. This also fixes "python setup.py install"
in the case that numpy is not installed already (same reason).

dseuss/mpnum,dseuss/mpnum