message: backend: fix protobuf to a specific git commit
diff: @@ -5,7 +5,7 @@ project(external-protobuf)
  include(ExternalProject)
  set(ARG_GIT_REPOSITORY https://github.com/google/protobuf.git)
  -set(ARG_GIT_TAG master)
  +set(ARG_GIT_TAG ab95b1bc1eb964ee5f1fb48297344c5d37d35191)
  if(ANDROID)
  message(STATUS "Preparing external project \"protobuf\" for Android...")
  