Use GitHub actions instead of Travis/Sauce Labs

The ability to use Sauce Labs for pull requests has now stopped working,
as Travis warned about several years ago. Instead run our tests directly
on GitHub on their various virtual machines.

.github/workflows/deploy.yml

@@ -0,0 +1,16 @@
+name: Publish
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+      - run: npm install
+      - run: npm publish --access public
+        env:
+          NODE_AUTH_TOKEN: ${{secrets.NPM_TOKEN}}