simplify insertion sort

sorting/insertion_sort.go

@@ -19,8 +19,10 @@ func main() {
 
 	var i, j int
 	for i = 1; i < len(arr); i++ {
-		for j = i; j > 0 && arr[j] < arr[j-1]; j-- {
+		for j = 0; j < i; j++ {
-			arr[j], arr[j-1] = arr[j-1], arr[j]
+			if arr[j] > arr[i] {
+				arr[i], arr[j] = arr[j], arr[i]
+			}
 		}
 	}