fix golint path. (#124)

as title

Author: appleboy

Makefile

@@ -27,7 +27,7 @@ vet:
 .PHONY: lint
 lint:
 	@which golint > /dev/null; if [ $$? -ne 0 ]; then \
-		go get -u github.com/golang/lint/golint; \
+		go get -u golang.org/x/lint/golint; \
 	fi
 	for PKG in $(PACKAGES); do golint -set_exit_status $$PKG || exit 1; done;