[3.6] Fix the indentation in Extending Python code example (GH-3244) (GH-3250)

Code was indented with three spaces.
Fixed using four spaces.
(cherry picked from commit d9a2b99ac4)
This commit is contained in:
Mariatta 2017-08-30 23:11:02 -07:00 committed by GitHub
parent 095a421b16
commit b5db7bb9da