Fixing shebang on dependency installation script.
The script assumes bash isn't installed which means it shouldn't be run with it.
Fixing dependency installation command for Debian based systems.
 - Combining installation of requirements.
 - Fixing name of 'llvm-dev'.
 - Removing unnecessary dependency 'build-essential'.
Merge pull request #12 from TheAssassin/master

Fixes for get_dependencies.sh for Debian based systems.