this.refs not transformed to this.$refs and ref callbacks don't work

[nlieb]

As in the title, the React this.refs is not transformed to the equivalent Vue this.$refs.

Also, ref callbacks do not work (ie the api replacing string refs https://facebook.github.io/react/docs/refs-and-the-dom.html#legacy-api-string-refs). This is important since ref strings are removed in React 16.x

For example this common React idiom won't work: <canvas ref={c => this.canvasRef = c} />

Fantastic idea and work so far. If I have time I'll try and get a pull request in.