Update Github request closer script to v3 of API.

Fixes bug #1012310

Github disabled v1 and v2 of their API permanently, forcing us to
update the script that closes Github pull requests to v3 of the API.
Update the script using the PyGithub lib.

Change-Id: I90c9faacdb7a72a470b8ad6aaea674edd9b8329e
1 file changed