Migrate to new GitHub Actions (#13)

Author: fwilhe

Diff for: .github/main.workflow

@@ -0,0 +1,15 @@
+on: push
+name: Lint all Dockerfiles
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Haskell Dockerfile Linter
+      uses: docker://cdssnc/docker-lint-github-action
+      with:
+        # https://github.com/hadolint/hadolint/wiki/DL3008
+        # https://github.com/hadolint/hadolint/wiki/DL3013
+        # https://github.com/hadolint/hadolint/wiki/DL3016
+        # https://github.com/hadolint/hadolint/wiki/DL3018
+        args: --ignore DL3008 --ignore DL3013 --ignore DL3016 --ignore DL3018