Use short array syntax for generated options

[pfrenssen]

When generating a form the resulting code is formatted with the short array syntax everywhere, but the options for a select form field are still using the old syntax:

    $form['category'] = [
      '#type' => 'select',
      '#title' => $this->t('Category'),
      '#options' => array('Technical problem / bug report' => $this->t('Technical problem / bug report')),
      '#size' => 5,
    ];

This PR ensures that short array syntax is also used for the select options.

[jmolivas]

@pfrenssen nice catch. Another PR fixes templates but this was left behind.

[jmolivas]

@pfrenssen Thanks for your contribution, your PR was merged. This will be included on the next release.