Support for the express@5.x

A new version of Express.js was recently released.
Unfortunately, the serverless-express does not support the new version.

The main issue occurs during request parsing with the body-parser. After updating to version 5.x, the request body is not parsed, and we receive a Buffer instance as the body

Start by reproducing the request-parsing problem in serverless-express with express@5.x and body-parser, then inspect the request parsing entry point. Compare the behavior with express 4.x and add coverage for the reported request body; done means Express 5 requests produce the parsed body instead of a Buffer.

Scritto dal modello di indicizzazione a partire dal testo della issue.