Use download mode for update-go-deps

Add `-d` to go get to avoid trying to build/install packages when
running `make update-go-deps`. Tested with 1.14.

Signed-off-by: SuperQ <superq@gmail.com>

Makefile.common

@@ -160,7 +160,7 @@ endif
 update-go-deps:
 	@echo ">> updating Go dependencies"
 	@for m in $$($(GO) list -mod=readonly -m -f '{{ if and (not .Indirect) (not .Main)}}{{.Path}}{{end}}' all); do \
-		$(GO) get $$m; \
+		$(GO) get -d $$m; \
 	done
 	GO111MODULE=$(GO111MODULE) $(GO) mod tidy
 ifneq (,$(wildcard vendor))