Support running on AWS Lambda and Google Cloud Functions

[joschi]

With bulldozer being an event-driven application (like most GitHub apps), it would be great if we could deploy it on AWS Lambda or GCP Cloud Functions.

For Probot, there are a few extensions to support these serverless deployment models:

• https://github.com/probot/serverless-lambda
• https://github.com/probot/serverless-gcf
• https://github.com/tibdex/probot-serverless-now

[abemedia]

This is already possible using https://github.com/awslabs/aws-lambda-go-api-proxy

[abemedia]

I was wrong. Seems the app is not stateless so Lambda doesn't work...

I tried and failed: #224