"Deploy to Heroku" Button

I have published an example to http://python-instagram.herokuapp.com/ but the app.json file expect this to be hosted at https://github.com/Instagram/python-instagram

The workaround was to push my "Heroku" branch as the "master" branch on Heroku i.e. 
```
git push heroku Heroku:master
```
Also, the following environment variables need to be configured on Heroku:
```
heroku config:set CLIENT_ID=[insert from http://instagram.com/developer/clients/manage/]
heroku config:set CLIENT_SECRET=[insert from http://instagram.com/developer/clients/manage/]
heroku config:set REDIRECT_URI=[insert from http://instagram.com/developer/clients/manage/]
```
The alternative is to "override" the environment variables using their Platform API but it is not possible to obfuscate "CLIENT_ID" and "CLIENT_SECRET" yet.

"python tests.py" output below:
```
..........................
----------------------------------------------------------------------
Ran 26 tests in 0.385s

OK
```
I've completed the Contributor License Agreement ("CLA") too.