fix build node package

tools/run_tests/build_package_node.sh

@@ -86,6 +86,7 @@ for arch in {x86,x64}; do
     cp $input_dir/protoc* bin/
     cp $input_dir/grpc_node_plugin* bin/
     mkdir -p bin/google/protobuf
+    mkdir -p bin/google/protobuf/compiler  # needed for plugin.proto
     for proto in "${well_known_protos[@]}"; do
       cp $base/third_party/protobuf/src/google/protobuf/$proto.proto bin/google/protobuf/$proto.proto
     done