Working with Postgres Jsonb

I'm trying to integrate Toucan into a project that uses Postgres, but I can't insert into a Jsonb column. Here's the model:
```
(m/add-type! :json
:in json/generate-string
:out #(json/parse-string % keyword))

(m/defmodel Integration :integrations
m/IModel
(m/types [_]
{:data :json}))
```
And here's the error:
```
user=> (db/insert! Integration {:registration "123" :data {"a" "b"}})
(db/insert! Integration {:registration "123" :data {"a" "b"}})
2019-04-09 19:04:13,218 [nRepl-session-f8c664bb-fa71-4a5c-b061-be9ef18ff331] DEBUG toucan.db - DB Call: INSERT INTO "integrations" ("registration", "data") VALUES (?, ())
Execution error (PSQLException) at org.postgresql.core.v3.QueryExecutorImpl/receiveErrorResponse (QueryExecutorImpl.java:2477).
ERROR: syntax error at or near ")"
Position: 66
```
I've followed the docs to the letter, but it doesn't work. Thanks!

@camsaul

Start with the `m/add-type!` JSON registration, the `Integration` model's `:data :json` type, and the `db/insert!` call shown in the report. Reproduce the generated INSERT against PostgreSQL and determine what change is needed for the Jsonb value to be inserted without the reported syntax error.

Written by the indexing model from the issue text.