update tree for new default type rule

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5448091

src/pkg/strings/strings.go

@@ -434,7 +434,7 @@ func Title(s string) string {
 	// Use a closure here to remember state.
 	// Hackish but effective. Depends on Map scanning in order and calling
 	// the closure once per rune.
-	prev := rune(' ')
+	prev := ' '
 	return Map(
 		func(r rune) rune {
 			if isSeparator(prev) {