go.tools/cmd/godoc: permit dash and capitals in redirect paths

This was causing some /blog/foo-bar-baz paths to 404.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/13640044

cmd/godoc/handlers.go

@@ -165,7 +165,7 @@ func makeRedirectHandler(target string) http.HandlerFunc {
 	}
 }
 
-var validId = regexp.MustCompile(`^[a-z0-9]*$`)
+var validId = regexp.MustCompile(`^[A-Za-z0-9-]*$`)
 
 func makePrefixRedirectHandler(prefix, baseURL string) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {