Fix missing include file "SmartLibgit2Ref.h"

it needs to be included after git2.h

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>
Not count in the directories in the working tree and files under .git directory

Signed-off-by: Yue Lin Ho <b8732003@student.nsysu.edu.tw>