Fix lingering usage of matplotlib.numerix

[scottza]

Fix lingering usage of matplotlib.numerix

scott@godzilla:PyTOPKAPI$ grep -rn "matplotlib.numerix" .
./pytopkapi/parameter_utils/map_param.py:8:    import matplotlib.numerix.ma as M
./pytopkapi/parameter_utils/map_param.py:41:    import matplotlib.numerix.ma as M

Thanks to Michael Benjamin for prompting me to look (https://groups.google.com/forum/#!topic/pytopkapi/RWVXrOqYuzI)