Fix typo in removing deprecated api endpoint

Description

Github deprecated and api endpoint for auth tokens on apps, I previously typed apps/ and it should have been app/

This has been tested by running the broken container, verifying that it did not work, then changing the apps to app and re-deploying - then invoking a change on github that sent webhooks to my installation. After the fix it worked, was given the 5k/hr rate limit and correctly added / removed labels from PRs.

There are also some logging improvements and the wrong error was being used for one of the print statements.

Signed-off-by: Alistair Hey alistair@heyal.co.uk

Motivation and Context

[x] I have raised an issue to propose this change (required)
156

How Has This Been Tested?

see commit message and text above

Types of changes

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[ ] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[ ] I've read the CONTRIBUTION guide
[ ] I have signed-off my commits with git commit -s
[ ] I have added tests to cover my changes.
[ ] All new and existing tests passed.

alexellis / derek