Refactor mutable borrowing in move_semantics5.rs

exercises/06_move_semantics/move_semantics5.rs

@@ -5,15 +5,19 @@
 //
 // Execute `rustlings hint move_semantics5` or use the `hint` watch subcommand
 // for a hint.
-
-// I AM NOT DONE
+// [[NOTE]] 使用作用域讓可變借用的生命週期提早結束
 
 #[test]
 fn main() {
-    let mut x = 100;
-    let y = &mut x;
-    let z = &mut x;
-    *y += 100;
-    *z += 1000;
+    let mut x = 100; 
+    {
+        let y = &mut x;
+        *y += 100;
+    }
+
+    {
+        let z = &mut x;
+        *z += 1000;
+    }
     assert_eq!(x, 1200);
 }