Change occurrences of master to main

Test: TreeHugger
Change-Id: Ie1641bb55f0df3f8c778a12d77b18b5a184c986e
diff --git a/github_archive_updater.py b/github_archive_updater.py
index 09110c1..e67d77b 100644
--- a/github_archive_updater.py
+++ b/github_archive_updater.py
@@ -144,7 +144,7 @@
         self._new_url.value = choose_best_url(urls, self._old_url.value)
 
     def _fetch_latest_commit(self) -> None:
-        """Checks upstream and gets the latest commit to master."""
+        """Checks upstream and gets the latest commit to default branch."""
 
         # pylint: disable=line-too-long
         branch = git_utils.detect_default_branch(self._proj_path,