6631003: Add hg tip changeset to build image

Reviewed-by: mduigou
diff --git a/.hgignore b/.hgignore
index 2d339f9..8fde2ca 100644
--- a/.hgignore
+++ b/.hgignore
@@ -2,3 +2,4 @@
 ^dist/
 /nbproject/private/
 ^webrev
+^.hgtip