Implement a function birdsInWeek that accepts an array of bird counts per day and a week number. It returns the total number of birds that you counted in that specific week. You can assume weeks are always tracked completely.
function birdsInWeek(birdsPerDay, week) {
}
birdsPerDay = [2, 5, 0, 7, 4, 1, 3, 0, 2, 5, 0, 1, 3, 1];
birdsInWeek(birdsPerDay, 2);
// => 12