simplify recipe for mln/version.hh
This fixes issues with (re)building milena. (See https://circleci.com/gh/OCR-D/ocrd_olena/31 or https://travis-ci.org/OCR-D/ocrd_olena/builds/656958262 for examples.)
This fixes issues with (re)building milena. (See https://circleci.com/gh/OCR-D/ocrd_olena/31 or https://travis-ci.org/OCR-D/ocrd_olena/builds/656958262 for examples.)