Fix trailing whitespace

Author: mzabaluev

src/libcore/result.rs

@@ -1081,7 +1081,7 @@ impl<T, E: Into<!>> Result<T, E> {
     /// ```
     /// # #![feature(never_type)]
     /// # #![feature(unwrap_infallible)]
-    /// 
+    ///
     /// fn only_good_news() -> Result<String, !> {
     ///     Ok("this is fine".into())
     /// }