grpcurl describe: proto import failure

command:
```
grpcurl \
-import-path dir/schema/protobuf/test \
-import-path github.com/googleapis/google/type/money.proto \
-proto dir/schema/protobuf/test/test.proto \
describe prototest.Price.FetchPriceByArticleId
```
output:
`Failed to process proto source files.: could not parse given files: test.proto:8:8: open dir/schema/protobuf/test/google/type/money.proto: no such file or directory`

working directory is parent for both `dir` and `github.com`

dir/schema/protobuf/test/test.proto
```
syntax = "proto3";
package test;

import "google/type/money.proto";
import "google/rpc/status.proto";

service Prices {
rpc FetchPriceByArticleId (FetchPriceByArticleIdRequest) returns (FetchPriceByArticleIdResponse) {};
}

message FetchPriceByArticleIdRequest {
google.type.Money price_supply = 1;
google.type.Money price_retail = 2;
}

message FetchPriceByArticleIdResponse {
google.rpc.Status status = 1;
google.type.Money price_retail = 2;
}
```