keep probot's app directory updated

[cyberhck]

for now I've done probot/probot.github.io#304 but I'm planning to contribute a cleanup where we'll simply remove the app for app directory if tests fail for more than a few days :)

[maks-rafalko]

Thanks. The fact that the build on some repository fails because of my nickname looks weird for me..

Anyway, thanks for your contribution.