This allow the bundle to be used in jsfiddle, plnkr, jsbin, etc.,
as the bundle does not depend on Vue.
The problem lies on second line of bundle
```js
"object" == typeof exports ? exports["vue-js-modal"] = factory(require("vue")) : root["vue-js-modal"] = factory(root.vue)
```
where `factory` tries to find `root.vue`, but the official Vue bundle exports
as `root.Vue`.
Removing the runtime dependency solves this.
`Object.assign` is available in all browsers but IE:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign