change aframe serve to dev

[caseyyee]

just to be more consistent with where we want to head with this (dev environment)

[cvan]

if it's cool, for now, I'm going to alias aframe dev to aframe serve (à la ionic serve).

and we can remove the alias and add a separate aframe dev command for running the server + connecting to a device (instructions would be provided, if not already paired – à la ionic cordova run).

the developer will then be able to send commands for which URLs to open, etc. on the developer's mobile device (i.e., using adb for Android or WebSockets for iOS, etc.).

[cvan]

I've filed issue #76 to handle the new aframe dev (alias: aframe run) command. I'll take this issue now (and resolve it) to handle the temporary alias of aframe dev → aframe serve.