error with input type="range" and v-model

The following code:
```
	render(h) {
		return <input type="range" v-model={this.opacity}/>;
	},
```

fails with:
```
Module build failed (from ../node_modules/babel-loader/lib/index.js):
Cannot read property 'toLowerCase' of undefined
```

whereas replacing `type="range"` with `type="number"` works fine.
