Docstrings out of sync: default value of arg use_local_webserver

[TrentonBush]

Thanks for your work maintaining this repo, I appreciate it! The following is a minor docstring issue I noticed.

The default value of use_local_webserver in pydata_google_auth/auth.py:get_user_credentials changed from False to True back around 1.3 to 1.4, but the docstring was never updated. The same arg, and its default value and out of date docstring seems to appear in several other functions in that module.

[tswast]

Thanks for the feedback! We're accepting contributions. :-)