add publish step

.github/workflows/ci.yaml

@@ -30,3 +30,28 @@ jobs:
     - run: pytest -c pytest.python3.ini  --cov-report= --cov=augur
     - run: cram --shell=/bin/bash tests/functional/*.t tests/builds/*.t
     - run: bash tests/builds/runner.sh
+  publish:
+    if: ${{ github.ref == 'refs/heads/release' }}
+    needs: [test]
+    runs-on: ubuntu-latest
+    steps:
+      - env:
+          TRAVIS_AUTH_TOKEN: ${{ secrets.TRAVIS_AUTH_TOKEN }}
+        run: |
+          set -euo pipefail
+
+          echo "Pinging Travis CI to rebuild Docker image"
+
+          body='{
+            "request": {
+              "branch": "master",
+              "message": "Build triggered from augur"
+            }
+          }'
+
+          curl -X POST https://api.travis-ci.com/repo/nextstrain%2Fdocker-base/requests \
+            -H "Content-Type: application/json" \
+            -H "Accept: application/json" \
+            -H "Travis-API-Version: 3" \
+            -H "Authorization: token $TRAVIS_AUTH_TOKEN" \
+            -d "$body"