travis: deploy sdist to Github on tags

Fixes #98

wheels are already uploaded to PyPI and automatically consumed by pip.

.travis.yml

@@ -90,6 +90,7 @@ after_success:
   - pip install tox
   # upload code coverage to Codecov.io
   - tox -e codecov
+  # deploy to PyPI on tags
   - |
     if [ -n "$TRAVIS_TAG" ] && [ "$TRAVIS_REPO_SLUG" == "adobe-type-tools/psautohint" ]; then
       pip install --upgrade twine
@@ -99,3 +100,17 @@ after_success:
         twine upload dist/psautohint*.zip
       fi
     fi
+
+deploy:
+  # deploy to Github Releases on tags
+  provider: releases
+  api_key:
+    secure: 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
+  skip_cleanup: true
+  file_glob: true
+  file: "dist/psautohint*.zip"
+  on:
+    tags: true
+    repo: adobe-type-tools/psautohint
+    all_branches: true
+    condition: "$BUILD_SDIST == true"