update kali_setup.sh

This should fix error's when script called from outside of install directory by directly specifying the path. here we are identifying the directory of script and then going one level up. Correct me if this is wrong approach.
Merge pull request #121 from anantshri/patch-1

update kali_setup.sh amended to work independently from the directory the setup script is called from. Thanks to Anant Shrivastava for noticing and fixing this