Use html_url field instead of url (GH-17)

The `html_url` field takes us to the actual comment on GitHub.
`url` field took us to an API JSON response.

Author: Mariatta

backport/util.py

@@ -20,7 +20,7 @@ def comment_on_pr(issue_number, message):
                              headers=request_headers,
                              json=data)
     if response.status_code == requests.codes.created:
-        print(f"Commented at {response.json()['url']}")
+        print(f"Commented at {response.json()['html_url']}")
     else:
         print(response.status_code)
         print(response.text)
@@ -36,4 +36,4 @@ def is_cpython_repo():
         subprocess.check_output(cmd.split(), stderr=subprocess.STDOUT)
     except subprocess.SubprocessError:
         return False
-    return True
+    return True