Updates to requests 1.1.0 API

In the recent requests, json retrieval is now a function call instead of attribute access. This pull request includes 3 fixes to get the example running with the latest API server and requests:

- Fix for .json -> .json()
- Specify library versions in requirements to be forward compatible for any future changes
- Use port 5000 for the server. The API seems to use this for callbacks even if 2323 is specified in redirect_uri.

Thanks for this great example code.