iOS target rather than iPhone/iPad

Since the repl is about testing the javascript/browser/DOM, the distinction between iphone/ipad doesn't seem too important.

My testing has mostly been about trying older/newer versions of mobile safari for compatibility, regardless of device name and model.

I was thinking of adding an `ios` target with versions 8,7,6 available. It'd use the iPhone.

Does that sound reasonable?

(We could explore deprecating iphone/ipad but that gets a bit more complicated.)