Apply 'pathname' to the first argument

[agatan]

Using cl-project via roswell script in SBCL and CLISP, an type mismatch error occurs.
While cl-project:make-project requires a pathname value as the first argument, in the script, the first argument is of type string.

To fix it, the first argument (it is specified from command line arguments) should be applied pathname function and I added it.

[madand]

The issue is more cleanly resolved by #22. Since the underlying call of uiop:ensure-directory-pathname actually supports string input.