Clean up E0701 explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0701.md

@@ -1,7 +1,7 @@
 This error indicates that a `#[non_exhaustive]` attribute was incorrectly placed
 on something other than a struct or enum.
 
-Examples of erroneous code:
+Erroneous code example:
 
 ```compile_fail,E0701
 #[non_exhaustive]