Use grpc-gateway fork for code generation.
Use grpc-gateway fork for code generation.

This fork uses the correct JSON names as specified by the Protobuf to
JSON mapping
(https://developers.google.com/protocol-buffers/docs/proto3#json).

This is needed until
https://github.com/grpc-ecosystem/grpc-gateway/pull/681 has been merged.

brocaar/lora-app-server,brocaar/lora-app-server,brocaar/lora-app-server,brocaar/lora-app-server