Update getting started tutorial for hapi v19

[devinivy]

The contents of the tutorial should mostly be fine for hapi v19, but it was reported that the way route validations are written causes an error from hapi. It is likely related to the need to define a validator or to wrap the validations in Joi.object(). See more info in the v19 release notes related to the "joi Schemas Compiler": hapijs/hapi#4017.