face_tracker_control package in chap 2

[mahshah]

thank you of Mr. Joseph Lentin for his worthwhile book. i want to share my experience.
it is necessary to add "face_tracker_pkg" in CmakeLists.txt of face_tracker_control package in chap 2, otherwise you will face with an error indicated that "face_tracker_pkg/centroid.h file not found"
find_package(catkin REQUIRED COMPONENTS
dynamixel_controllers
roscpp
rospy
message_generation
std_msgs
face_tracker_pkg
)