allow linebreaks in the config_current_fahrt_id file to reduce confusion

registration-system/frameworks/Environment.php

@@ -189,7 +189,7 @@ class Environment {
     private function readCurrentTripId() {
         global $config_current_fahrt_file;
         if (file_exists($config_current_fahrt_file)) {
-            $tmp = file_get_contents($config_current_fahrt_file);
+            $tmp = trim(file_get_contents($config_current_fahrt_file));
             if (is_numeric($tmp))
                 return $tmp;
         }