Fix defined type namespacing

Without this patch, puppet 4 apply tests can't find the drush defined type
and fail with:

  Evaluation Error: Resource type not found: Drush at /etc/puppetlabs/code/modules/drupal/manifests/init.pp:241:38

This patch ensures the resource reference is namespaced properly.

Change-Id: Ibd1972c681085344a36c51951f32aa3e93e501c8

manifests/init.pp

@@ -238,7 +238,7 @@ class drupal (
     mode    => '0400',
     content => template('drupal/aliases.drushrc.php.erb'),
     replace => true,
-    require => [ File['/etc/drush'], Drush['drush'] ],
+    require => [ File['/etc/drush'], Drupal::Drush['drush'] ],
   }
 
   # site custom configuration