Upgrade json schema to latest version

We've been using 1.1.1 for a long time, and 2.2.5 brings some fancy new features like strict mode. With this upgrade, we'll be able to depend the newer json-schema version in apps that use interpol.
I'll declare it out of scope for now. There's a `$schema` key you can use to point to a specific schema version, but I'm not sure how the `json-schema` gem handles that when also passed an explicit `version` key.