var banner = new Array();
banner[0]='https://i.imgur.com/bIRni.png';
banner[1]='https://i.imgur.com/IgG5e.png';



document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];

setInterval("document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];",3000);