book: it is RwLock, not RWLock

Author: tshepang

src/doc/trpl/choosing-your-guarantees.md

@@ -40,7 +40,7 @@ allowed to share references to this by the regular borrowing rules, checked at c
 
 [box]: ../std/boxed/struct.Box.html
 
-## `&T` and `&mut T` 
+## `&T` and `&mut T`
 
 These are immutable and mutable references respectively. They follow the “read-write lock”
 pattern, such that one may either have only one mutable reference to some data, or any number of
@@ -243,7 +243,7 @@ Many of the types above cannot be used in a threadsafe manner. Particularly, `Rc
 `RefCell<T>`, which both use non-atomic reference counts (_atomic_ reference counts are those which
 can be incremented from multiple threads without causing a data race), cannot be used this way. This
 makes them cheaper to use, but we need thread safe versions of these too. They exist, in the form of
-`Arc<T>` and `Mutex<T>`/`RWLock<T>`
+`Arc<T>` and `Mutex<T>`/`RwLock<T>`
 
 Note that the non-threadsafe types _cannot_ be sent between threads, and this is checked at compile
 time.