added build script

Author: maxpaj

package.json

@@ -4,6 +4,7 @@
  "description": "Vue plugin for Keen.io tracking",
  "main": "index.js",
  "scripts": {
+ "build": "webpack --config build/webpack.config.js",
  "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [