book: fix typo in 03-runtime.md (changkun#95)

HaoyuanLuo · changkun · commit 89060d4b9669 · 2020-03-15T15:13:20.000+01:00
fix chapter3.7 perfect.forward code err.
diff --git a/book/zh-cn/03-runtime.md b/book/zh-cn/03-runtime.md
@@ -470,7 +470,7 @@ void pass(T&& v) {
     std::cout << "    std::forward 传参: ";
     reference(std::forward<T>(v));
     std::cout << "static_cast<T&&> 传参: ";
-    reference(std::forward<T>(v));
+    reference(static_cast<T&&>(v));
 }
 int main() {
     std::cout << "传递右值:" << std::endl;
