[Bug] Fix wrong contents of 8.4 and add sample code

eBook/examples/chapter_8/maps_forrange2.go

@@ -0,0 +1,21 @@
+package main
+
+import "fmt"
+
+func main() {
+	// Version A:
+	items := make([]map[int]int, 5)
+	for i := range items {
+		items[i] = make(map[int]int, 1)
+		items[i][1] = 2
+	}
+	fmt.Printf("Version A: Value of items: %v\n", items)
+
+	// Version B: NOT GOOD!
+	items2 := make([]map[int]int, 5)
+	for _, item := range items2 {
+		item = make(map[int]int, 1) // item is only a copy of the slice element.
+		item[1] = 2                 // This 'item' will be lost on the next iteration.
+	}
+	fmt.Printf("Version B: Value of items: %v\n", items2)
+}