MNT: Fix errors from flake8-docstring
MNT: Fix errors from flake8-docstring

pydocstyle 2.1.0 broke API, breaking flake8-docstrings. Pinning should
fix this for now.

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