define open and closed mobile state
$('button.navbar-toggle').on('click', function(){
setTimeout(open_menu, 50);
});
var open_menu = function(){
if ( !$('.navbar-toggle').hasClass('collapsed') ) {
$('.navbar-toggle').addClass('menu_open');
console.log('open');
} else {
$('.navbar-toggle').removeClass('menu_open');
console.log('closed');
}
};