Symbol not found: grpc.reflection.v1alpha.ServerReflection

On a server with reflection enabled (works fine with both grpcurl and grpcox), I get this error when running grpcui:

```
$ grpcui -vvv -bind 0.0.0.0 -port 8082 -plaintext localhost:4567
INFO: 2019/06/14 10:49:37 parsed scheme: ""
INFO: 2019/06/14 10:49:37 scheme "" not registered, fallback to default scheme
INFO: 2019/06/14 10:49:37 ccResolverWrapper: sending update to cc: {[{localhost:4567 0 }] }
INFO: 2019/06/14 10:49:37 ClientConn switching balancer to "pick_first"
INFO: 2019/06/14 10:49:37 pickfirstBalancer: HandleSubConnStateChange: 0xc00006ee30, CONNECTING
INFO: 2019/06/14 10:49:37 pickfirstBalancer: HandleSubConnStateChange: 0xc00006ee30, READY
Failed to compute set of methods to expose: Symbol not found: grpc.reflection.v1alpha.ServerReflection
```