Fix extra argument in readme.md

Author: stefangordon

README.md

@@ -123,7 +123,7 @@ To use `rtabmap_ros` on Jetson, you can follow the instructions above if you don
     $ cd ~/catkin_ws
     $ git clone https://github.com/ros-perception/vision_opencv src/vision_opencv
     $ git clone https://github.com/ros-perception/image_transport_plugins.git src/image_transport_plugins
-    $ git clone https://github.com/introlab/rtabmap_ros.git src/rtabmap_ros src/rtabmap_ros
+    $ git clone https://github.com/introlab/rtabmap_ros.git src/rtabmap_ros
     $ catkin_make -j2
    ```