book: fix smart pointers (changkun#90)

bud-adamas · changkun · commit e5450c767cd9 · 2020-01-08T07:09:27.000+01:00
diff --git a/book/zh-cn/05-pointers.md b/book/zh-cn/05-pointers.md
@@ -160,8 +160,8 @@ struct B {
 int main() {
     auto a = std::make_shared<A>();
     auto b = std::make_shared<B>();
-    a.pointer = b;
-    b.pointer = a;
+    a->pointer = b;
+    b->pointer = a;
 }
 ```
 
