Fix Docker perm issue on Linux

This changes the Docker command to run as the current user, it also sets
the HOME directory to /tmp as /root wouldn't be writable but is
still needed for Go cache files.

Refs: dcos/dcos-core-cli#347

Makefile

@@ -62,7 +62,8 @@ else
   define inDocker
     docker run \
       -e GOFLAGS \
-      -e GO111MODULE \
+      -e GOFLAGS -e GO111MODULE -e HOME=/tmp \
+      -u $(shell id -u):$(shell id -g) \
       -v $(CURRENT_DIR):$(PKG_DIR) \
       -w $(PKG_DIR) \
       --rm \