Fix method name in Lecture 04 slide snippet

Co-authored-by: teodositashev<[email protected]>

04-collections-clean-code/lecture/slides.md

@@ -1103,7 +1103,7 @@ public static long factorial(int n) { // business logic
 }
 
 public static void main(String... args) {
- int input = readAndValidate(new Scanner(System.in));
+ int input = readInput(new Scanner(System.in));
  long result = factorial(input);
  printOutput(result);
 }