grovel: use INVOKE rather than ASDF/RUN-PROGRAM in PKG-FLAGS
grovel: use INVOKE rather than ASDF/RUN-PROGRAM in PKG-FLAGS

Fixes issue #50.

3b/cffi,attila-lendvai/cffi,cffi/cffi,stassats/cffi,mcna/cffi,3b/cffi,dkochmanski/cffi,cffi/cffi,dkochmanski/cffi,mcna/cffi,stassats/cffi,cffi/cffi,dkochmanski/cffi,3b/cffi,stassats/cffi,attila-lendvai/cffi