MNT: Build examples with matplotlib < 2.1 for now
MNT: Build examples with matplotlib < 2.1 for now

Matplotlib 2.1.0 is causing problems with CartoPy maps.

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