fix(min_and_max): correct placeholder in example

subjects/min_and_max/README.md

@@ -18,7 +18,7 @@ use min_and_max::min_and_max;
 
 fn main() {
     println!(
-        "Minium and maximum are: ${?}",
+        "Minium and maximum are: ${:?}",
         min_and_max(9, 2, 4)
     );
 }