Update src/libcore/option.rs

Co-authored-by: Steve Klabnik <steve@steveklabnik.com>

src/libcore/option.rs

@@ -1399,7 +1399,7 @@ impl<'a, T> From<&'a Option<T>> for Option<&'a T> {
 
 #[stable(feature = "option_ref_from_ref_option", since = "1.30.0")]
 impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T> {
-    /// Converts from &mut Option<T> to Option<&mut T>
+    /// Converts from `&mut Option<T>` to `Option<&mut T>`
     ///
     /// # Examples
     ///