hackdoc: when redirecting, skip ref if default

Change-Id: Ie1680500ede673c407c9c8f4bbbe6b7f6a41b422
diff --git a/devtools/hackdoc/markdown.go b/devtools/hackdoc/markdown.go
index 5004642..8923545 100644
--- a/devtools/hackdoc/markdown.go
+++ b/devtools/hackdoc/markdown.go
@@ -21,7 +21,7 @@
 
 	// master is the default branch - do not make special links for that, as
 	// that makes them kinda ugly.
-	if ref == "master" {
+	if ref == flagGitwebDefaultBranch {
 		ref = ""
 	}