Fix arena iteration to use slices instead of lengths

gol/arena.go

@@ -32,9 +32,9 @@ func (a Arena) PrintMe() {
 	b := bufPool.Get().(*bytes.Buffer)
 	b.Reset()
 
-	for i := range len(a) {
+	for i := range a {
-		for j := range len(a[0]) {
+		for _, v := range a[i] {
-			if a[i][j] {
+			if v {
 				b.Write(spriteOn)
 			} else {
 				b.Write(spriteOff)
@@ -47,8 +47,8 @@ func (a Arena) PrintMe() {
 }
 
 func (a Arena) NextGen(to Arena) {
-	for y := range len(a) {
+	for y := range a {
-		for x := range len(a[0]) {
+		for x := range a[y] {
 			to[y][x] = a.life(x, y)
 		}
 	}