book: revise the description of RAII (#288)

Author: Mq-b

book/en-us/07-thread.md

@@ -35,7 +35,7 @@ C++11 introduces a class related to `mutex`, with all related functions in the `
 It can be locked by its member function `lock()`, and `unlock()` can be unlocked.
 But in the process of actually writing the code, it is best not to directly call the member function,
 Because calling member functions, you need to call `unlock()` at the exit of each critical section, and of course, exceptions.
-At this time, C++11 also provides a template class `std::lock_guard` for the RAII syntax for the mutex.
+At this time, C++11 also provides a template class `std::lock_guard` for the RAII mechanism for the mutex.
 
 RAII guarantees the exceptional security of the code while keeping the simplicity of the code.
 

book/zh-cn/07-thread.md

@@ -35,7 +35,8 @@ C++11 引入了 `mutex` 相关的类，其所有相关的函数都放在 `<mutex
 而通过其成员函数 `lock()` 可以进行上锁，`unlock()` 可以进行解锁。
 但是在实际编写代码的过程中，最好不去直接调用成员函数，
 因为调用成员函数就需要在每个临界区的出口处调用 `unlock()`，当然，还包括异常。
-这时候 C++11 还为互斥量提供了一个 RAII 语法的模板类 `std::lock_guard`。
+而 C++11 为互斥量提供了一个 RAII 机制的模板类 `std::lock_guard`。
+
 RAII 在不失代码简洁性的同时，很好的保证了代码的异常安全性。
 
 在 RAII 用法下，对于临界区的互斥量的创建只需要在作用域的开始部分，例如：