time: run TestTicker for longer during short test, otherwise it fails

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5671049

src/pkg/time/tick_test.go

@@ -13,7 +13,7 @@ func TestTicker(t *testing.T) {
 	const Count = 10
 	Delta := 100 * Millisecond
 	if testing.Short() {
-		Delta = 10 * Millisecond
+		Delta = 20 * Millisecond
 	}
 	ticker := NewTicker(Delta)
 	t0 := Now()