book: use curly brackets to initailize aggregate objects (#112)

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Author: TinyWang

book/en-us/02-usability.md

@@ -426,10 +426,10 @@ auto arr = new auto(10); // arr as int *
 > In addition, `auto` cannot be used to derive array types:
 > 
 > ```cpp
-> auto auto_arr2[10] = arr;   // illegal, can't infer array type
+> auto auto_arr2[10] = {arr};   // illegal, can't infer array type
 >
 > 2.6.auto.cpp:30:19: error: 'auto_arr2' declared as array of 'auto'
->     auto auto_arr2[10] = arr;
+>     auto auto_arr2[10] = {arr};
 > ```
 
 ### decltype

book/zh-cn/02-usability.md

@@ -361,10 +361,10 @@ auto arr = new auto(10); // arr 被推导为 int *
 > 此外，`auto` 还不能用于推导数组类型：
 >
 > ```cpp
-> auto auto_arr2[10] = arr;   // 错误,  无法推导数组元素类型
+> auto auto_arr2[10] = {arr};   // 错误,  无法推导数组元素类型
 >
 > 2.6.auto.cpp:30:19: error: 'auto_arr2' declared as array of 'auto'
->     auto auto_arr2[10] = arr;
+>     auto auto_arr2[10] = {arr};
 > ```
 
 ### decltype