Fix issue 903 Cannot access protected propert when drush generate-makefi...

Happen in Drush 7

PHP Fatal error: Cannot access protected property Drupal\Core\Extension\Extension::$filename in /home/username/.composer/vendor/drush/drush/commands/make/generate.make.inc on line 169

Solution:

Change generate.make.inc line 167 - 169

$project['_type'] = $extension->getType();
$project['type'] = $extension->getType();
$info_file = $extension->getFilename();

https://github.com/drush-ops/drush/issues/903