unused_macro_rules switched used and unused comments

Author: ralpha

compiler/rustc_lint_defs/src/builtin.rs

@@ -1032,8 +1032,8 @@ declare_lint! {
     /// ```rust
     /// #[warn(unused_macro_rules)]
     /// macro_rules! unused_empty {
-    ///     (hello) => { println!("Hello, world!") }; // This rule is unused
-    ///     () => { println!("empty") }; // This rule is used
+    ///     (hello) => { println!("Hello, world!") }; // This rule is used
+    ///     () => { println!("empty") }; // This rule is unused
     /// }
     ///
     /// fn main() {