setupTodos using incorrect logic and skipping to-do item.

[rhijjawi]

After looking over #703, I realized that todo.default(elems[i]) in page.js was overwriting elements while still reading over them in the loop.

export default function(element) {
    element.swapWith(
        Todo(element.dataset.todoId)
    )
}

This causes a Todo element to "disappear" as it takes the position of the overwritten element and being skipped in the iteration.

The fix is to create a copy of the element array so that it is maintained while changes are being made to the document.

[svilenmarkov]

Thanks for contributing!