Update marshmallow to 3.20.2#601

pyup-bot wants to merge 1 commit intomasterRobotStudio/bors:masterfrom

pyup-update-marshmallow-3.2.1-to-3.20.2RobotStudio/bors:pyup-update-marshmallow-3.2.1-to-3.20.2Copy head branch name to clipboard