add prepare

Author: casperlamboo

package.json

@@ -6,6 +6,7 @@
   "scripts": {
     "start": "webpack-dev-server -w",
     "test": "echo \"Error: no test specified\" && exit 1",
+    "prepare": "npm run build",
     "build": "npm run build:main && npm run build:module",
     "build:main": "BABEL_ENV=main babel src -s -d lib",
     "build:module": "BABEL_ENV=module babel src -s -d module"