docs: update examples in Jupyter Notebooks

Author: chilango74

.travis.yml

@@ -11,8 +11,6 @@ install:
   - pip install ipykernel
 # command to run tests
 script:
-  - python -m ipykernel install --user --name py39
-  - pytest --nbmake examples
   - pytest tests --cov=okama/
 after_success:
   - coveralls