Scenarios - Web - Heroku: link rot

* http://devcenter.heroku.com/articles/python redirects to https://devcenter.heroku.com/articles/getting-started-with-python - this is resolved in d7e3519fc4ad828f3534864d8d38e9ccbc9aa2bd.
* python.herokuapp.com no longer exists - python.heroku.com, however, redirects to the "Python" category of Heroku's documentation. I added that link to the section.
  - If python.herokuapp.com still exists, I'd be more than happy to revise the PR.