use struct update syntax in with_step()

ranges.v

@@ -32,10 +32,8 @@ pub fn (mut r Range[T]) reset() {
 // with_step returns copy of the range with new step value.
 pub fn (r Range[T]) with_step[T](step T) Range[T] {
 	return Range[T]{
-		start:  r.start
-		end:    r.end
+		...r
 		step: step
-		is_neg: r.is_neg
 		cur:  r.start
 	}
 }