[DOC] Added author name back (pyjanitor-devs#1056)

Author name fell off of docs during the move from readthedocs to sphinx

Author: robertmitchellv

AUTHORS.md

@@ -102,3 +102,4 @@ Contributors
 - [@fireddd](https://github.com/fireddd) |  [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3Afireddd)
 - [@Zeroto521](https://github.com/Zeroto521) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/pulls?utf8=%E2%9C%93&q=is%3Aclosed+mentions%3Zeroto521)
 - [@thatlittleboy](https://github.com/thatlittleboy) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3Athatlittleboy)
+- [@robertmitchellv](https://github.com/robertmitchellv) | [contributions](https://github.com/pyjanitor-devs/pyjanitor/issues?q=is%3Aclosed+mentions%3Arobertmitchellv)