Add support for GitHub Actions

[j-f1]

Details:

• Ci name: GitHub Actions
• Website: https://github.com/features/actions
• Default env variables: https://developer.github.com/actions/creating-github-actions/accessing-the-runtime-environment/#environment-variables

Environment variables

Environment variables example

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=fb1d0264fdb4
GITHUB_ACTION=Env
GITHUB_ACTOR=j-f1
GITHUB_EVENT_NAME=push
GITHUB_EVENT_PATH=/github/workflow/event.json
GITHUB_REPOSITORY=j-f1/eslint-docs
GITHUB_SHA=50141211ee907a2f592f03d99caf45c131fb6782
GITHUB_WORKFLOW=Run tests
GITHUB_WORKSPACE=/github/workspace
HOME=/github/home
GITHUB_REF=refs/heads/tmp

Additional context
It would be nice to add support for this before it gets out of beta.

[fishcharlie]

Especially since GitHub Actions added support for CI/CD this would be especially helpful. @watson

[ethomson]

See #42

[sibiraj-s]

Fixed in #42