E0206 - code review changes

compiler/rustc_error_codes/src/error_codes/E0206.md

@@ -1,4 +1,5 @@
-The `Copy` trait was implemented on a type which is neither a struct nor an enum nor a union.
+The `Copy` trait was implemented on a type which is neither a struct, an 
+enum, nor a union.
 
 Erroneous code example:
 
@@ -9,6 +10,6 @@ struct Bar;
 impl Copy for &'static mut Bar { } // error!
 ```
 
-You can only implement `Copy` for a struct, a union, or an enum.
+You can only implement `Copy` for a struct, an enum, or a union.
 The previous example will fail because `&'static mut Bar`
-is not a struct or enum.
+is not a struct, an enum, or a union.