Fix ueberauth_github sample.

[ramortegui]

This PR updates the libraries related with ueberauth_github issue and solves https://github.com/ueberauth/ueberauth_example/issues/23

On heroku sample app:

Locally I was able to reproduce it:

After updating libraries:

[ramortegui]

@doomspork great!. Any chance to re-deploy the heroku app? ( to test it ;) )

[doomspork]

@ramortegui it should be autodeploying now, just give it a few minutes to get there 😁

[ramortegui]

@doomspork I checked the app on heroku, and still isn't working. So, I deployed the master branch in heroku: https://warm-chamber-41439.herokuapp.com/ and I configure it using a custom oauth app. (see config below), and is working.

Could you check the github app? (credentials, urls, logs)

Thanks ;)

[ramortegui]

@doomspork any chance to look up the github app❓