Update src/sim/plugins/CMakeLists.txt

src/sim/plugins/CMakeLists.txt

+cmake_minimum_required(VERSION 2.8 FATAL_ERROR)
+
+find_package(gazebo REQUIRED)
+include_directories(${GAZEBO_INCLUDE_DIRS})
+link_directories(${GAZEBO_LIBRARY_DIRS})
+list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")
+
+add_library(hello_world SHARED hello_world.cc)
+target_link_libraries(hello_world ${GAZEBO_LIBRARIES})
+add_library(model_push SHARED model_push.cc)
+target_link_libraries(model_push ${GAZEBO_LIBRARIES})