Clean up E0459 explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0459.md

@@ -1,4 +1,6 @@
-A link was used without a name parameter. Erroneous code example:
+A link was used without a name parameter.
+
+Erroneous code example:
 
 ```compile_fail,E0459
 #[link(kind = "dylib")] extern {}