message: Replaced var with const in docs
diff: @@ -355,7 +355,7 @@ chart.subscribeClick(function(param) {
  Takes a screenshot of the whole chart.
  ```javascript
  -var screenshot = chart.takeScreenshot();
  +const screenshot = chart.takeScreenshot();
  ```
  The function returns a `canvas` element with the chart drawn on it. Any `Canvas` methods like `toDataURL()` or `toBlob()` can be used to serialize the result.
  