Fix incorrect description of E0690

Author: aticu

src/librustc_error_codes/error_codes/E0690.md

@@ -14,7 +14,7 @@ struct LengthWithUnit<U> { // error: transparent struct needs exactly one
 Because transparent structs are represented exactly like one of their fields at
 run time, said field must be uniquely determined. If there is no field, or if
 there are multiple fields, it is not clear how the struct should be represented.
-Note that fields of zero-typed types (e.g., `PhantomData`) can also exist
+Note that fields of zero-sized types (e.g., `PhantomData`) can also exist
 alongside the field that contains the actual data, they do not count for this
 error. When generic types are involved (as in the above example), an error is
 reported because the type parameter could be non-zero-sized.