fix: fixes the bug when defer or async attribute set in the html "script...

how to reproduce bug  in google chrome
```html
<script defer src='/libs/mapbox-gl.js'></script>
<script defer src='any_other_lib.js'></script>
```

---

modern browsers support [document.currentScript] property   
we need this fix

[document.currentScript]:https://developer.mozilla.org/en/docs/Web/API/document.currentScript