Update mpl version check to use string comparisons
Update mpl version check to use string comparisons

ShawnMurd/MetPy,ahaberlie/MetPy,dopplershift/MetPy,Unidata/MetPy,Unidata/MetPy,jrleeman/MetPy,dopplershift/MetPy,ahaberlie/MetPy,jrleeman/MetPy