DOC: Fixed GL02 errors in documentation
Fixed 2 of the 4 GL02 errors generated by pandas_validation_errors.ipynb 
The remaining two errors are from pandas.Timestamp.isoweekday and will be tackled next. 

is there a linter check we're going to add for this? xref https://github.com/pandas-dev/pandas/issues/25120
 Thanks @fshi01. Happy to have you to tackle the remaining GL02 errors and add a check in our CI.  In addition to the remaining GL02 errors and adding a check to the CI, is there anything else I should do before it is merged?  Nothing in particular.