message: remove "(devel)" label in the README
diff: OSPRay
  ======
  -This is release v1.8.0 (devel) of OSPRay. For changes and new features
  +This is release v1.8.0 of OSPRay. For changes and new features
  see the [changelog](CHANGELOG.md). Visit http://www.ospray.org for more
  information.
  