Improve upload to pypi

- avoid error if file already exists (apparently it can happen)
- disable progressbar as is useless on CI

Author: ssbarnea

tox.ini

@@ -93,4 +93,4 @@ envdir={toxworkdir}/lint
 deps={[testenv:lint]deps}
 commands =
     {[testenv:lint]commands}
-    twine upload --verbose dist/*
+    twine upload --disable-progress-bar --skip-existing --verbose dist/*