Remove :Z from volume mount.

Author: jdoss

Makefile

@@ -147,7 +147,7 @@ release:
 		-e GORELEASER_KEY=${GORELEASER_KEY} \
 		-e GPG_PRIVATE_KEY_FILE=${GPG_PRIVATE_KEY_FILE} \
 		--entrypoint /go/src/$(PKG)/docker/build/entrypoint.sh \
-		-v ${GPG_PRIVATE_KEY_FILE}:${GPG_PRIVATE_KEY_FILE}:Z \
+		-v ${GPG_PRIVATE_KEY_FILE}:${GPG_PRIVATE_KEY_FILE} \
 		-v $(DOCKER_SOCK):/var/run/docker.sock:Z \
 		-v `pwd`:/go/src/$(PKG):Z \
 		-w /go/src/$(PKG) \