led circleci-bash image

Docker image to test bash script with CircleCI

It's an extension of CircleCI Golang image https://hub.docker.com/r/circleci/golang/

Includes

• shellcheck A tool that gives warnings and suggestions for bash/sh shell scripts https://github.com/koalaman/shellcheck
• shfmt A shell parser, formatter and interpreter. https://github.com/mvdan/sh