Changed version.txt location to a relative path

Fixes #62 (For real)

In 8e9bc51 we began pulling the version number from a tracked file instead
of hard-coding it into SetList.vi, but I never changed the path to the
version to a relative path instead of the hard-coded test path used
locally.  This fixes that, now encoding the position of version.txt
relative to SetList.vi.

Tested by running SetList from two other locations on my hard drive,
successfully saved and loaded with version numbers from all 3 places.