Why doesn't my favicon appear?

I want to add a favicon to my github.io page but it will not appear. I amhosting my favicon on dropbox as a .png. My code on my index.html page is:

<link rel="shortcut icon" href="https://www.dropbox.com/s/5dt587axxwvj2ft/arg_favicon.png?dl=0" type="image/x-icon">
<link rel="icon" href="/favicon.ico" type="image/x-icon">

Solution

updated based on asker's comment

All you really need is:

<link rel="icon" href="//photos-3.dropbox.com/t/2/AADgf5ha0ZRZ9q_VZGT9I6cP9Sk27rCN26PvVDe82RKGgg/12/207862012/png/1024x768/3/1420758000/0/2/arg_favicon.png/CPzxjmMgAyACIAEoAigB/gPsvlZzDk2FAwU_MD5BJvE_4GAbCtJg6ORwdcMq1esQ">

EDIT I've created a page for you with your icon hosted on github and here is the link and code: http://grandstaffdesign.com/ITO/test.html

<html>
<head>
<title>test page</title>
<link rel="icon" href="//photos-3.dropbox.com/t/2/AADgf5ha0ZRZ9q_VZGT9I6cP9Sk27rCN26PvVDe82RKGgg/12/207862012/png/1024x768/3/1420758000/0/2/arg_favicon.png/CPzxjmMgAyACIAEoAigB/gPsvlZzDk2FAwU_MD5BJvE_4GAbCtJg6ORwdcMq1esQ">
</head>
<body>
Answer for cbunn
</body>
</html>

insight I was able to get your link working by using the actual link of the image. The one you left in the comment was a php redirect that displays the image indirectly.