Fix collection of gid of Docker socket

src/Handler.php

@@ -233,7 +233,7 @@ class Handler extends BaseHandler {
     $this->config->setValue('relatedprojectdomains', $relatedprojectdomains, FALSE);
 
     // Get ID of Docker group
-    $docker_group_id = shell_exec('stat -c "%g" /var/run/docker.sock');
+    $docker_group_id = trim(shell_exec('stat -c "%g" /var/run/docker.sock'));
     $this->config->setValue('docker_group_id', $docker_group_id, FALSE);
 
     if ($alerta_api_key = getenv('ALERTA_APIKEY')) {