The Display URL is the website address visible in a click ad. The actual destination URL isn’t necessarily the same (though it can’t be too different to be acceptable to Google).
Up until now you could capitalize your display URL as you wished, for emphasis, easy remembering or to clearly communicate what the URL means.

www.FastF.com

That’s no longer true:

www.thirteen05.com

You can, however, still capitalize the page name if you are sending someone to an interior page. So all is not lost:

www.thirteen05.com/Website-Design-Portfolio

This is NOT a popular change. We’ll see if it sticks.