apollo-server-hapi: replace deprecated hapi by @hapi/hapi

[mblottiere]

This aims to fix #3132

[abernix]

This attempts the same/similar update as #3089 which we reverted in #3111. Unfortunately, because of the dropping of Node.js 6 support, we'll have to reject it for the same reasons noted in #3111.

Without bumping the major version of Apollo Server to 3.x, there's no semver-correct way to release this under the 2.x umbrella. I realize this is problematic, but this is exactly the reason that we are introducing the concept of transports (see #3184) that can be versioned separately and live outside of Apollo Server core.