BUG: Fixed github stats retrieval

Currently urllib is used to retrieve a json file from Github, however
Github url used is not static url, urllib2 required to retrieve
information from Github.

Author: Carwyn Pelley

tools/github_stats.py

@@ -13,7 +13,7 @@
 
 from datetime import datetime, timedelta
 from subprocess import check_output
-from urllib import urlopen
+from urllib2 import urlopen
 
 #-----------------------------------------------------------------------------
 # Globals