fix link on std::result::Result

The link is broken here: <https://doc.rust-lang.org/std/io/#types>.

Looks like crate documentation generator uses only first paragraph of the module documentation and 
so doesn't resolve the link defined below.

src/libstd/io/error.rs

@@ -17,9 +17,8 @@ use option::Option::{self, Some, None};
 use result;
 use sys;
 
-/// A specialized [`Result`][result] type for I/O operations.
-///
-/// [result]: ../result/enum.Result.html
+/// A specialized [`Result`](../result/enum.Result.html) type for I/O 
+/// operations.
 ///
 /// This type is broadly used across `std::io` for any operation which may
 /// produce an error.