Use structured suggestion for braceless unicode escape squence

src/libsyntax_ext/format.rs

@@ -845,8 +845,8 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt,
                             }
                         } else if next_c.is_digit(16) {
                             skips.push(next_pos);
-                            // We suggest adding `{` and `}` when appropriate, accept it here as if it
-                            // were correct
+                            // We suggest adding `{` and `}` when appropriate, accept it here as if
+                            // it were correct
                             let mut i = 0;  // consume up to 6 hexanumeric chars
                             while let (Some((next_pos, c)), _) = (s.next(), i < 6) {
                                 if c.is_digit(16) {