Update jaegertracing/protobuf to 0.4.0 (#99)

Signed-off-by: Matthieu MOREL <[email protected]>

Makefile

@@ -11,7 +11,7 @@ PROTOTOOL_VER=1.8.0
 PROTOTOOL_IMAGE=uber/prototool:$(PROTOTOOL_VER)
 PROTOTOOL=docker run --rm -u ${shell id -u} -v "${PWD}:/go/src/${PROJECT_ROOT}" -w /go/src/${PROJECT_ROOT} $(PROTOTOOL_IMAGE)
 
-PROTOC_VER=0.3.1
+PROTOC_VER=0.4.0
 PROTOC_IMAGE=jaegertracing/protobuf:$(PROTOC_VER)
 PROTOC=docker run --rm -u ${shell id -u} -v "${PWD}:${PWD}" -w ${PWD} ${PROTOC_IMAGE} --proto_path=${PWD}