message: update version to v2.0
diff: ## limitations under the License. ##
  ## ======================================================================== ##
  -set(OSPRAY_VERSION_MAJOR 1)
  -set(OSPRAY_VERSION_MINOR 8)
  +set(OSPRAY_VERSION_MAJOR 2)
  +set(OSPRAY_VERSION_MINOR 0)
  set(OSPRAY_VERSION_PATCH 0)
  set(OSPRAY_SOVERSION 0)
  set(OSPRAY_VERSION_GITHASH 0)
  