Removed the --inorder option from the spawn to avoid the warning when launching Gazebo.

launch/description.launch

@@ -6,7 +6,7 @@
 
   <group ns="$(arg name)">
     <param name="robot_description"
-           command="$(find xacro)/xacro --inorder '$(find model_car_description)/urdf/car.xacro' name:=$(arg name) sim_config_path:=$(arg sim_config_path)" />
+           command="$(find xacro)/xacro '$(find model_car_description)/urdf/car.xacro' name:=$(arg name) sim_config_path:=$(arg sim_config_path)" />
 
     <node pkg="robot_state_publisher" type="robot_state_publisher" name="tf_broadcaster_$(arg name)">
       <param name="publish_frequency" type="double" value="50.0"/>