Modernize Dockerfile #251

	name: Docker

	on:
	push:
	# Publish `master` as Docker `latest` image.
	branches:
	- master

	# Publish `v1.2.3` tags as releases.
	tags:
	- v*

	# Run tests for any PRs.
	pull_request:

	env:
	IMAGE_NAME: nsjail

	jobs:
	# Run tests.
	# See also https://docs.docker.com/docker-hub/builds/automated-testing/
	test:
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v2

	- name: Run tests
	run: docker build . --file Dockerfile

	# Push image to GitHub Package Registry.
	# See also https://docs.docker.com/docker-hub/builds/
	push:
	# Ensure test job passes before pushing image.
	needs: test

	runs-on: ubuntu-latest
	if: github.event_name == 'push'

	steps:
	- uses: actions/checkout@v2

	- name: Build image
	run: docker build . --file Dockerfile --tag image

	- name: Log into registry
	run: echo "${{ secrets.GITHUB_TOKEN }}" \| docker login docker.pkg.github.com -u ${{ github.actor }} --password-stdin

	- name: Push image
	run: \|
	IMAGE_ID=docker.pkg.github.com/${{ github.repository }}/$IMAGE_NAME

	# Strip git ref prefix from version
	VERSION=$(echo "${{ github.ref }}" \| sed -e 's,./$.$,\1,')

	# Strip "v" prefix from tag name
	[[ "${{ github.ref }}" == "refs/tags/"* ]] && VERSION=$(echo $VERSION \| sed -e 's/^v//')

	# Use Docker `latest` tag convention
	[ "$VERSION" == "master" ] && VERSION=latest

	echo IMAGE_ID=$IMAGE_ID
	echo VERSION=$VERSION

	docker tag image $IMAGE_ID:$VERSION
	docker push $IMAGE_ID:$VERSION

Provide feedback