message: [c++ grpc] Pass --init to update gRPC submodules
  Sometimes gRPC adds new submodule dependencies, so we need to pass the
  `--init` flag to `git submodule update` so that new submodules are
  initialized.
diff: @@ -7,7 +7,7 @@ pushd "$BOND_ROOT/thirdparty/grpc"
  git fetch origin master
  git checkout origin/master
  git submodule sync --recursive
  -git submodule update --recursive
  +git submodule update --init --recursive
  popd
  BOND_CMAKE_FLAGS="$BOND_CMAKE_FLAGS -DBOND_SKIP_GBC_TESTS=TRUE -DBOND_SKIP_CORE_TESTS=TRUE -DgRPC_ZLIB_PROVIDER=package"
  