(#108) Modulefile should chdir before calling git

This change request modifies Modulefile to chdir into the root of the
project before executing git. This is necessary to get the version number
of the project but fails when called outside of the directory:

  fatal: Not a git repository (or any parent up to mount parent )
  Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).

The change is desirable to work with other projects, like librarian-puppet
in particular that fails with an unhelpful error message because of the
exception raised in the Modulefile.