docs: fix typo cc -> c in List.forEachWithIndex example

Author: mikaello

src/Core__List.resi

@@ -432,7 +432,7 @@ List.forEachWithIndex(list{"a", "b", "c"}, (x, index) => {
   prints:
   Item 0 is a
   Item 1 is b
-  Item 2 is cc
+  Item 2 is c
 */
 ```
 */