I'm trying to create a custom Quill theme, extending the bubble one. I'm facing a strange ES6 inheritance problem, where it seems I cannot call `super()` in my constructor. Here is my code:

```
import BubbleTheme, { BubbleTooltip } from 'quill/themes/bubble'

class LoopTheme extends BubbleTheme {
  constructor (quill, options) {
    super(quill, options)
  }

  extendToolbar (toolbar) {
    super.extendToolbar(toolbar)
    this.tooltip = new LoopTooltip(this.quill, this.options.bounds);
    this.tooltip.root.appendChild(toolbar.container);
  }
}

class LoopTooltip extends BubbleTooltip {

}

LoopTooltip.TEMPLATE = [
  '<span class="ql-tooltip-arrow"></span>',
  '<div class="ql-tooltip-editor">',
    '<input type="text" data-formula="e=mc^2" data-link="https://myurl.com" data-video="Embed URL">',
    '<a class="ql-close"></a>',
  '</div>'
].join('');

export { LoopTooltip, LoopTheme as default }

```

Bubble theme could be found [here](https://github.com/quilljs/quill/blob/develop/themes/bubble.js)

My Babel presets:

```
{
    "presets": [
        "es2015",
        "es2016",
        "stage-0",
        "react"
    ]
}

```

Webpack js file config:

```
  module: {
    rules: [
      {
        test: /\.js$/,
        include: [
          resolve(__dirname, 'app')
        ],
        loader: 'babel-loader',
        exclude: /node_modules/
      }, {...

```

Output generated code:

```
var LoopTheme = function (_BubbleTheme) {
  _inherits(LoopTheme, _BubbleTheme);

  function LoopTheme() {
    _classCallCheck(this, LoopTheme);

    return _possibleConstructorReturn(this, (LoopTheme.__proto__ || Object.getPrototypeOf(LoopTheme)).apply(this, arguments));
  }

  _createClass(LoopTheme, [{
    key: 'extendToolbar',
    value: function extendToolbar(toolbar) {
      _get(LoopTheme.prototype.__proto__ || Object.getPrototypeOf(LoopTheme.prototype), 'extendToolbar', this).call(this, toolbar);
      this.tooltip = new LoopTooltip(this.quill, this.options.bounds);
      this.tooltip.root.appendChild(toolbar.container);
    }
  }]);

  return LoopTheme;
}(_bubble2.default);

var LoopTooltip = function (_BubbleTooltip) {
  _inherits(LoopTooltip, _BubbleTooltip);

  function LoopTooltip() {
    _classCallCheck(this, LoopTooltip);

    return _possibleConstructorReturn(this, (LoopTooltip.__proto__ || Object.getPrototypeOf(LoopTooltip)).apply(this, arguments));
  }

  return LoopTooltip;
}(_bubble.BubbleTooltip);

LoopTooltip.TEMPLATE = ['<span class="ql-tooltip-arrow"></span>', '<div class="ql-tooltip-editor">', '<input type="text" data-formula="e=mc^2" data-link="myurl.com" data-video="Embed URL">', '<a class="ql-close"></a>', '</div>'].join('');

exports.LoopTooltip = LoopTooltip;
exports.default = LoopTheme;

```

I'm having the following error: `events.js:59 Uncaught TypeError: Class constructor BubbleTheme cannot be invoked without 'new'`. However, the `LoopTheme` is correctly called with `new` by Quill [here](https://github.com/quilljs/quill/blob/develop/core/quill.js#L84). When I debug step by step, I correctly enter the `LoopTheme` constructor, and the error is raised when `super` is called.

Am I missing something here? I've always used inheritance, and I use it elsewhere in my code (between my classes), where here am I having trouble?

Thanks for your help