Explicitly require emacs 24
Explicitly require emacs 24

The code uses `lexical-binding`, so although `js2-mode` depends on Emacs 24, it's best if `skewer-mode` also makes the dependency explicit.

kostafey/skewer-mode,emacsmirror/skewer-mode,skeeto/skewer-mode,syohex/skewer-mode,syohex/skewer-mode,skeeto/skewer-mode,emacsmirror/skewer-mode,kostafey/skewer-mode