Typo for commit 9a0ecfa8c, EP8 find library

[yhan048]

Hi, thanks so much for your cmake tutorials.
I think there is a tiny typo in EP8, find library.
9a0ecfa
in the main.cpp file, line 5
#include <GL/glut.h> may need to change into
#include <GL/glu.h>
since we didn't find the glut lib