Add trailing newline

Author: aelred

src/test/compile-fail/must_use-in-stdlib-traits.rs

@@ -44,4 +44,4 @@ fn main() {
    square_fn_once(); //~ ERROR unused implementer of `std::ops::FnOnce` that must be used
    square_fn_mut(); //~ ERROR unused implementer of `std::ops::FnMut` that must be used
    square_fn(); //~ ERROR unused implementer of `std::ops::Fn` that must be used
-}
+}