day05 performance push part 2 through more efficient case insensitive comparison

src/tasks/day05.rs

@@ -22,7 +22,7 @@ pub fn task2() {
                 reduce(
                     &input
                         .chars()
-                        .filter(|ch| ch.to_lowercase().next().unwrap() != c)
+                        .filter(|ch| ch.eq_ignore_ascii_case(&c))
                         .collect::<String>(),
                 ).len(),
             )