channels: sum up to positive

TinyGo can't quite handle a negative result, so switch the
channels example to sum up to something positive.

channels/main.go

@@ -13,7 +13,7 @@ func sum(s []int, c chan int) {
 }
 
 func main() {
-	s := []int{7, 2, 8, -9, 4, 0}
+	s := []int{7, 2, 8, 9, -4, 0}
 
 	c := make(chan int)
 	go sum(s[:len(s)/2], c)