add navigation active as page scroll

script.js

$(function(){
  $(window).scroll(function(){
    var windscroll = $(window).scrollTop();
    $('body .section').each(function(i){
      if ($(this).position().top <= windscroll){
        $('nav li.active').removeClass('active');
        $('nav li').eq(i).addClass('active');
      };
    });
  });
});