MNT: Update appveyor config.
MNT: Update appveyor config.

Specify kernel to use to run notebooks.

jrleeman/MetPy,ahill818/MetPy,dopplershift/MetPy,jrleeman/MetPy,Unidata/MetPy,deeplycloudy/MetPy,Unidata/MetPy,ahaberlie/MetPy,ShawnMurd/MetPy,ahaberlie/MetPy,dopplershift/MetPy