[damned-lies] Add mainline to the list of HEAD branch names

[Claude Paroz <claudep src gnome org>]

commit 5dbbeb0a404d6d5de4454202d86ad4fcbe773639
Author: Michael James Gratton <mike vee net>
Date:   Tue Apr 2 16:25:48 2019 +1100

    Add mainline to the list of HEAD branch names

 stats/models.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/stats/models.py b/stats/models.py
index 9c4f4ac9..93c022e1 100644
--- a/stats/models.py
+++ b/stats/models.py
@@ -70,7 +70,8 @@ VCS_TYPE_CHOICES = (
 BRANCH_HEAD_NAMES = (
     'HEAD',
     'trunk',
-    'master'
+    'mainline',
+    'master',
 )