Update refs element usage
This release update the refs usage to the new api:
https://reactjs.org/docs/refs-and-the-dom.html
"Legacy API: String Refs
If you worked with React before, you might be familiar with an older API where the ref attribute is a string, like "textInput", and the DOM node is accessed as this.refs.textInput. We advise against it because string refs have some issues, are considered legacy, and are likely to be removed in one of the future releases. If you’re currently using this.refs.textInput to access refs, we recommend the callback pattern instead."
Thanks to @kunukn for contributing!