force upgrade to latest python deps in travis to fix tests

Author: telamonian

.travis.yml

@@ -14,7 +14,7 @@ script:
   # Install the extension from the sdist ensuring the cache is unused
   - pip install jupyterlab_git[test] --pre --no-index --find-links=dist --no-deps --no-cache-dir -v
   # Install the extension dependencies based on the current setup.py
-  - pip install jupyterlab_git[test]
+  - pip install --upgrade --upgrade-strategy=eager jupyterlab_git[test]
   # Log the current state of jupyterlab's extensions
   - jupyter labextension list