0.2.1

what

• Check Docker credentials in docker:login
• Don't login to Docker if credentials are missing

why

• For external PRs (not originating from the original repo), for security reasons CI environments like Travis don't provide the ENV vars specified in repo Settings, and Docker login fails

$ make docker:login
DOCKER_HUB_USERNAME not defined in docker:login
make: *** [docker:login] Error 1
The command "make docker:login" failed and exited with 2 during .