Fix working directory

SClang expects the working directory to be wherever the user started it from. This is important for loading resources, like this:

    cd ~/tracks/foo
    vi main.sc

    (
      // Should load ~/tracks/foo/foo.wav, but tries to load /usr/bin/foo.wav and fails
      Buffer.load("foo.wav")
    )

The patch restores this functionality.
Merge pull request #26 from carlocapocasa/patch-1

Fix working directory