Documentation fix date render element

API page: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21...

Enter a descriptive title (above) relating to class Date, then describe the problem you have found:

In the example that is provided, there is a missing ' in the default_value.

$form['expiration'] = [
      '#type' => 'date',
      '#title' => $this->t('Content expiration'),
      '#default_value' => 2020-02-05',
    ];

Should be:

$form['expiration'] = [
      '#type' => 'date',
      '#title' => $this->t('Content expiration'),
      '#default_value' => '2020-02-05',
    ];

Patch provided for code. Documentation page should be updated also.