Replace third-party mock with unittest.mock] vision/fair

Reviewed By: bottler

Differential Revision: D45600232

fbshipit-source-id: f41b95c6fca86d241666b54755a128cd33f6dd32

docs/conf.py

@@ -20,7 +20,8 @@
 import os
 import sys
 
-import mock
+import unittest.mock as mock
+
 from recommonmark.parser import CommonMarkParser
 from recommonmark.states import DummyStateMachine
 from sphinx.builders.html import StandaloneHTMLBuilder