fix(intro1.rs): typo in the exercise body

exercises/00_intro/intro1.rs

@@ -29,7 +29,7 @@ fn main() {
     println!("or logic error. The central concept behind Rustlings is to fix these errors and");
     println!("solve the exercises. Good luck!");
     println!();
-    println!("The source for this exercise is in `exercises/intro00/intro1.rs`. Have a look!");
+    println!("The source for this exercise is in `exercises/00_intro/intro1.rs`. Have a look!");
     println!(
         "Going forward, the source of the exercises will always be in the success/failure output."
     );