Enabling module fails on PHP Parse error

When enabling the module on a Drupal 7.54 site, I get a PHP parse error on Line 79:

$ drush @sitename en addtocalendar
The following extensions will be enabled: addtocalendar
Do you really want to continue? (y/n): y
PHP Parse error:  syntax error, unexpected '[' in /data/virtual/common/drupal/sites/all/modules/addtocalendar/addtocalendar.module on line 79
Drush command terminated abnormally due to an unrecoverable error.                                                                                                        [error]
Error: syntax error, unexpected '[' in /data/virtual/common/drupal/sites/all/modules/addtocalendar/addtocalendar.module, line 79

I inspected the (rather innocuous) line in question, which is here with some context:

...
71: $info = array(
72:   'atc_title' => t('Title'),
73:   'atc_description' => t('Description'),
74:   'atc_location' => t('Location'),
75:   'atc_organizer' => t('Organizer'),
76:   'atc_organizer_email' => t('Organizer email'),
77:   'atc_date_end' => t('End Date'),
78: );
79: $field_options = [];
80: foreach($field_list as $id => $field_i) {
81:   $field_options[$id] = $field_i['label'];
82: }
...

Seems like a valid line to me. I tried changing it to $field_options = array();, but no dice.

Any ideas why it's crashing on this line?