Bug 1569472 - Fix flake8 error in tools/docs/mach_commands.py r=championshuttler

Differential Revision: https://phabricator.services.mozilla.com/D42371

--HG--
extra : moz-landing-system : lando

tools/docs/mach_commands.py

@@ -9,6 +9,7 @@ import os
 import sys
 import multiprocessing
 from functools import partial
+from pprint import pprint
 
 from mozbuild.base import MachCommandBase
 from mach.decorators import (