Return proto3 go-grpc response: repeated message without message name

Question

Right now I have this proto file that specifies a grpc method that is also an http rest style api using go-grpc-gateway:

rpc GetBars(GetBarReq) returns (GetBarRes) {
    option (google.api.http) = {
        get : "/v1/bar"
    };
};

message Bar {
  string a = 1;
  string b = 2;
}

message GetBarRes {
  repeated Bar bar = 1;
}

message GetBarReq {
  string id = 1;
}

I have some golang app logic where I implement the generated structures.

func (s *barServer) GetBars(req *pb.GetBarReq) (*pb.GetBarRes, error) {
    ...
    return &pb.GetBarRes{Bars: bars}, nil
}

which returns:

{
"bars": [
    {
        "a": "a",
        "b": "b"
    },
    {
        "a": "a",
        "b": "b"
    }
]
}

How could I modify the proto file or my app logic to return this instead:

[
    {
        "a": "a",
        "b": "b"
    },
    {
        "a": "a",
        "b": "b"
    }
]