added -y option to docker_build.sh. I also fixed a bug on -p option

[masayang]

trafficstars

I had added a couple of features to the sample template. I also fixed a bug in docker_build.sh

• Now -p option works correctly.
• By providing -y option, you can specify a version of Python. Default is 3.8
• If pipenv is in the path, requirements.txt will be generated through pip freeze
• If jupyter is in the path, workflows/*.ipynb will be transformed to *.py files.

[welcome[bot]]

Thank you for opening this pull request! 🙌 These tips will help get your PR across the finish line: - Most of the repos have a PR template; if not, fill it out to the best of your knowledge. - Sign off your commits (Reference: DCO Guide).

[cosmicBboy]

also, @masayang would you mind following the instructions here for the DCO tests to pass? https://github.com/src-d/guide/blob/master/developer-community/fix-DCO.md