Minor annoyance: an unused import is generated for pg

Hi, thanks for this! It looks really useful.

I encountered a small issue with the 'pg' backend. This line is generated:

```typescript
import { IPostgresInterval } from "postgres-interval";
```

If it is not used, it is a compiler error when `noUnusedLocals` is on.

If it is difficult to selectively include, maybe add a `// @ts-ignore` annotation?