tests: Switch from Travis to Github Actions

Travis placed an unnecessary breaking restriction on our tests and failed to respond within 72 hours to our complaint.  This has forced us to introduce Github Actions to manage our testing.  This is hopefully a temporary measure while Travis either gets itself together or we find a non-Github requirement.

.github/workflows/dockerfile.yml

@@ -0,0 +1,26 @@
+name: "Dockerfile"
+
+# any branch is useful for testing before a PR is submitted
+on: [push, pull_request]
+
+jobs:
+  dockerfile:
+    # run on pushes to any branch
+    # run on PRs from external forks
+    if: |
+         (github.event_name != 'pull_request')
+         || (github.event.pull_request.head.repo.id != github.event.pull_request.base.repo.id)
+    name: build image and run connectivity test
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v2
+
+    - name: docker build
+      run: |
+        docker build -t etherpad:test .
+        docker run -d -p 9001:9001 etherpad:test
+        ./bin/installDeps.sh
+        sleep 3 # delay for startup?
+        cd src && npm run test-container