Use main branch as the default branch

R=apolito@google.com

Change-Id: I6a2ed557b9e8d45194b2fe4ea5327ce62020733c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3000134
Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
diff --git a/git_common.py b/git_common.py
index d70bdfb..8008c62 100644
--- a/git_common.py
+++ b/git_common.py
@@ -707,7 +707,7 @@
         pass
     return ret
   except subprocess2.CalledProcessError:
-    return 'origin/master'
+    return 'origin/main'
 
 
 def root():