add flake8 fail to github actions

Author: rflamary

.github/workflows/pythonpackage.yml

@@ -36,7 +36,7 @@ jobs:
         # stop the build if there are Python syntax errors or undefined names
         flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
-        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics        
+        flake8 examples/ ot/ test/ --count --max-line-length=127 --statistics        
     - name: Install POT
       run: |
         pip install -e .