[Emacs] Update emacs

Thanks @benedekfazekas for the info. @TheEternalPulse_twitter I've just installed Emacs 25 + spacemacs on Ubuntu 16.10 using the private package archive from https://launchpad.net/~kelleyk/+archive/ubuntu/emacs and it all seems to work (give the basic tests of running a repl & evaluating code). Certainly didnt get the if-let error this time.