Building Heroku-based application using gliderlabs/herokuish docker image... Attempting to pull a previously built image for use with --cache-from... invalid reference format invalid reference format No previously cached image found. The docker build will proceed without using a cached image invalid argument "/main:aea0da95e297c900e61fbb5d7ace4856f7571807" for "-t, --tag" flag: invalid reference format See 'docker build --help'. Cleaning up file based variables ERROR: Job failed: exit code 1