Drop support for objection@1

[JaneJeon]

1. I'm tired of seeing the deprecation message
2. New typings (esp. w/ Add typescript definition file #1) may be incompatible with the v1 typings
3. Dropping v1 support may let us use new features like static hooks. In particular, I'm interested in this: Unlike the instance query hooks, static hooks are executed once per query. Static hooks are always executed and there are no corner cases like the $beforeDelete/$afterDelete issue with instance hooks. http://vincit.github.io/objection.js/guide/hooks.html#static-query-hooks