add unistd.h for close() calling

hi teacher!
I am a student from your class "advanced programming in linux environment"
I downloaded the codes, and when I typed 'make' coCLSharedMemorymmad, I found that there is an error occurred.
so, I added <unistd.h> for close() calling in CLSharedMemory.cpp
and then, I 'make' successfully.
and now, I send this pull request to you.
I really glad to take your course and learn a lot of coding-techs in linux.
thank you very much!