fix wrapping

Author: MatthewPeterKelly

compiler/rustc_error_codes/src/error_codes/E0311.md

@@ -29,22 +29,21 @@ Rust book) to the `nested_borrow_mut` and `borrow_mut` functions. In both cases
 the input is a reference to `self`, so the compiler attempts to assign the
 the same lifetime to the input and output.
 
-Looking specifically at `nested_borrow_mut`,
-we see that there are three object references to keep track of,
-along with their associated lifetimes:
+Looking specifically at `nested_borrow_mut`, we see that there are three object
+references to keep track of, along with their associated lifetimes:
 - `self` (which is a `&mut T`)
 - `u_ref` (which is a `&mut U`)
 - `v_ref` (which is a `&mut V`)
 
 The `borrow_mut()` method implicitly requires that that the input and output
-have the same lifetime bounds. Thus:
+have the same lifetime bounds. Thus the lines:
 
 ```rust
         let u_ref = self.borrow_mut();
         let v_ref = u_ref.borrow_mut();
 ```
 
-Imply that `u_ref` and `self` must share a lifetime bound, and also that
+imply that `u_ref` and `self` must share a lifetime bound, and also that
 `v_ref` and `u_ref` share a lifetime bound. The problem is that the function
 signature for `nested_borrow_mut` only gives the compiler information about the
 lifetimes of `self` and `v_ref` -- nothing about `u_ref`.