Update README.md

Author: hsd-dev

README.md

@@ -3,7 +3,6 @@
 ## Installation
 ```
 $ cd <path/to/workspace/src> git clone -b nav_observer https://github.com/ipa-hsd/rosgraph_monitor/
-$ cd <path/to/workspace/src> git clone -b SoSymPaper https://github.com/ipa-nhg/ros_graph_parser
 $ cd <path/to/workspace>
 $ source /opt/ros/melodic/setup.bash
 $ rosdep install --from-paths src --ignore-src -r -y