Sequelize should be able to create transactions on read replica

## What you are doing?
```js
sequelize(..., {
    replication: {
        read: [REPLICA],
        write: PRIMARY
    }
})

sequelize.transaction(() => {
    /* Read-only stuff here that requires repeatable reads */
})
```

## What do you expect to happen?
The transaction should execute on the read replica.

## What is actually happening?
It executes on the write.
