Merge pull request #1815 from YangFong/patch-1

Update macros.md

src/macros.md

@@ -21,7 +21,7 @@ macro_rules! say_hello {
 }
 
 fn main() {
-    // This call will expand into `println!("Hello")`
+    // This call will expand into `println!("Hello!")`
     say_hello!()
 }
 ```