Fix 2fa for gh_stats tools.

tools/gh_api.py

@@ -17,7 +17,7 b' import json'
 try:
     import requests_cache
 except ImportError:
-    print("no cache", file=sys.stderr)
+    print("cache not available, install `requests_cache` for caching.", file=sys.stderr)
 else:
     requests_cache.install_cache("gh_api", expire_after=3600)
 

tools/github_stats.py

@@ -212,8 +212,7 b' if __name__ == "__main__":'
 
     print("We closed %d issues and merged %d pull requests." % (n_issues, n_pulls))
     if milestone:
-        print("The full list can be seen `on GitHub <https://github.com/%s/milestone/%s>`__"
-            % (project, milestone)
+        print("The full list can be seen `on GitHub <https://github.com/{project}/issues?q=milestone%3A{milestone}+>`__".format(project=project,milestone=milestone)
         )
     
     print()