fixed a typo in the reference to the example

src/ch01-03-hello-cargo.md

@@ -101,7 +101,7 @@ fn main() {
 ```
 
 Cargo has generated a “Hello, world!” program for you, just like the one we
-wrote in Listing 1-1! So far, the differences between our project and the
+wrote in Listing 1-2! So far, the differences between our project and the
 project Cargo generated are that Cargo placed the code in the *src* directory
 and we have a *Cargo.toml* configuration file in the top directory.