trpl: punctuation fix

src/doc/trpl/mutability.md

@@ -35,7 +35,7 @@ let y = &mut x;
 
 `y` is an immutable binding to a mutable reference, which means that you can’t
 bind `y` to something else (`y = &mut z`), but you can mutate the thing that’s
-bound to `y`. (`*y = 5`) A subtle distinction.
+bound to `y` (`*y = 5`). A subtle distinction.
 
 Of course, if you need both:
 

src/doc/trpl/patterns.md

@@ -66,7 +66,7 @@ match x {
 }
 ```
 
-This prints `something else`
+This prints `something else`.
 
 # Bindings
 
@@ -152,7 +152,7 @@ match x {
 }
 ```
 
-This prints `Got an int!`
+This prints `Got an int!`.
 
 # ref and ref mut