Code style improvements in JavaScript (#13159)

* JS-linter: fix trailing comma's

* Configure eslinter to ignore this onchange error.

app/javascript/mastodon/features/compose/components/poll_form.js

@@ -155,6 +155,7 @@ class PollForm extends ImmutablePureComponent {
         <div className='poll__footer'>
           <button disabled={options.size >= 4} className='button button-secondary' onClick={this.handleAddOption}><Icon id='plus' /> <FormattedMessage {...messages.add_option} /></button>
 
+          {/* eslint-disable-next-line jsx-a11y/no-onchange */}
           <select value={expiresIn} onChange={this.handleSelectDuration}>
             <option value={300}>{intl.formatMessage(messages.minutes, { number: 5 })}</option>
             <option value={1800}>{intl.formatMessage(messages.minutes, { number: 30 })}</option>