MNT: Fix pydocstyle version
MNT: Fix pydocstyle version

Also utilize EXTRA_PACKAGES for more of our one-off installs on Travis.

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