Add npm prepublish hook.

Author: wcjohnson

package.json

@@ -9,7 +9,8 @@
  "scripts": {
  "test": "mocha test",
  "test:debug": "node --inspect --debug-brk mocha test",
- "build": "babel src --out-dir ."
+ "build": "babel src --out-dir .",
+ "prepublish": "npm run build"
  },
  "author": "Alex Rattray <rattray.alex@gmail.com> (http://alexrattray.com/)",
  "homepage": "http://lightscript.org/",