Use git rev-parse to get nightly commit hash

publish.py

@@ -269,13 +269,7 @@ class GitHub(Base):  # {{{
     def update_nightly_description(self, release_id: int) -> None:
         url = f'{self.url_base}/{release_id}'
         now = str(datetime.datetime.utcnow()).split('.')[0] + ' UTC'
-        try:
-            with open('.git/refs/heads/master') as f:
-                commit = f.read().strip()
-        except FileNotFoundError:
-            time.sleep(1)
-            with open('.git/refs/heads/master') as f:
-                commit = f.read().strip()
+        commit = subprocess.check_output(['git', 'rev-parse', '--verify', '--end-of-options', 'master^{commit}']).decode('utf-8').strip()
         self.patch(
             url, 'Failed to update nightly release description',
             body=f'Nightly release, generated on: {now} from commit: {commit}.'