Fix error: add pcl lib to target_link_libraries

[smoggy-P]

When I try to build this repository, it throws the following error:

Errors     << exploration_manager:make /catkin_ws/logs/exploration_manager/build.make.007.log                   
/usr/bin/ld: CMakeFiles/exploration_node.dir/src/perception_aware_exploration_manager.cpp.o: undefined reference to symbol '_ZNK3pcl11KdTreeFLANNINS_8PointXYZEN5flann9L2_SimpleIfEEE12radiusSearchERKS1_dRSt6vectorIiSaIiEERS8_IfSaIfEEj'
/usr/bin/ld: /lib/x86_64-linux-gnu/libpcl_segmentation.so.1.10: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/exploration_node.dir/build.make:155: /catkin_ws/devel/.private/exploration_manager/lib/exploration_manager/exploration_node] Error 1
make[1]: *** [CMakeFiles/Makefile2:926: CMakeFiles/exploration_node.dir/all] Error 2
make: *** [Makefile:141: all] Error 2
cd /catkin_ws/build/exploration_manager; catkin build --get-env exploration_manager | catkin env -si  /usr/bin/make --jobserver-auth=3,4; cd -

It turns out that the PCL_LIBRARIES is not added to target_link_libraries. It is fixed in this commit.