Hapi v17 support
Thank you for creating the library; I enjoy using it with Hapi to authenticate my apps in Shopify stores.

[Hapi v17](https://github.com/hapijs/hapi/issues/3658) has introduced a lot of breaking changes and I can't make Grant Hapi plugin work with the new version.

Are you considering upgrading your Hapi plugin to support Hapi v17 in the near future? 