message: review updates:
  explicitly request MPI version 3.1
diff: @@ -15,7 +15,7 @@ if (NOT DEFINED GINKGO_BUILD_OMP)
  endif()
  if (NOT DEFINED GINKGO_BUILD_MPI)
  - find_package(MPI)
  + find_package(MPI 3.1)
  if(MPI_FOUND)
  message(STATUS "Enabling MPI support")
  set(GINKGO_HAS_MPI ON)
  