Minor fix for steer actuation controller for gazebo

Related to space-ros#49

curiosity_rover/curiosity_description/models/config/mars_rover_control.yaml

@@ -15,12 +15,11 @@ controller_manager:
       type: joint_trajectory_controller/JointTrajectoryController
 
     wheel_tree_position_controller:
-      type: effort_controllers/JointGroupPositionController
+      type: position_controllers/JointGroupPositionController
 
     joint_state_broadcaster:
       type: joint_state_broadcaster/JointStateBroadcaster
 
-
 arm_joint_trajectory_controller:
   ros__parameters:
     joints:
@@ -60,7 +59,6 @@ wheel_velocity_controller:
       - back_wheel_R_joint
     interface_name: velocity
 
-
 steer_position_controller:
   ros__parameters:
     joints: