Fails to build with postgres feature

[kanhirun]

Summary

I'm interested in using postgres for my database, but cargo build --features postgres fails with a type error. The solo-machine-core crate does support this as a feature, but isn't working as expected.

Replicating the error

1. Clone repo
2. cargo build --features postgres
3. Observe the following error:

...
error[E0271]: type mismatch resolving `<impl Executor<'e, Database = Db> as Executor<'_>>::Database == Sqlite`
   --> solo-machine-core/src/model/chain/chain_keys.rs:94:16
    |
94  |     .fetch_all(executor)
    |      --------- ^^^^^^^^ expected `Sqlite`, found `Postgres`
    |      |
    |      required by a bound introduced by this call
    |