www/py-webargs: Update to 6.1.1

Changelog: https://github.com/marshmallow-code/webargs/blob/dev/CHANGELOG.rst#611-2020-09-08

PR: 249220
Submitted by: Goran Mekic <meka@tilda.center> (maintainer)
MFH: 2020Q3 (blanket: bugfix release)