$(document).ready(function(){
  var url = window.location;
  // Will only work if string in href matches with location
  $('ul.nav a[href="'+ url +'"]').parent().addClass('active');

  // Will also work for relative and absolute hrefs
  $('ul.nav a').filter(function() {
      return this.href == url;
  }).parent().addClass('active');  
});