diff -urN ../libcalendaring.orig/libcalendaring.php ./libcalendaring.php
--- ../libcalendaring.orig/libcalendaring.php	2017-01-18 14:58:47.000000000 +0200
+++ ./libcalendaring.php	2017-01-18 18:02:11.000000000 +0200
@@ -29,6 +29,8 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
+require_once(__DIR__ . '/vendor/autoload.php');
+
 class libcalendaring extends rcube_plugin
 {
     public $rc;