message: Fixes custom BBox usage with latest update
  The drag.html example was broken.
diff: @@ -1045,9 +1045,11 @@ export default class Sigma extends EventEmitter {
  * @return {Dimensions}
  */
  getGraphDimensions(): Dimensions {
  + const extent = this.customBBox || this.nodeExtent;
  +
  return {
  - width: this.nodeExtent.x[1] - this.nodeExtent.x[0],
  - height: this.nodeExtent.y[1] - this.nodeExtent.y[0],
  + width: extent.x[1] - extent.x[0],
  + height: extent.y[1] - extent.y[0],
  };
  }
  