Cannot add primary key with addColumn

Some years ago this same issue came up in https://github.com/db-migrate/node-db-migrate/issues/408. This was fixed by adding a check for a null `options` param:

```
if (spec.primaryKey) {
if (!options || options.emitPrimaryKey) {
constraint.push('PRIMARY KEY');
}
}
```

A year later the call to `createColumnDef` from `addColumn` was changed to pass `{}` instead of `null` as `options`, which means this check always fails and the `PRIMARY KEY` constraint is never added. If you add an autoincrement field you are unable to set it as a primary key, resulting in the migration always failing with this error:

```
ER_WRONG_AUTO_KEY: Incorrect table definition; there can be only one auto column and it must be defined as a key
```

I have a PR to check for an empty object instead in the mysql adapter. This could be fixed upstream by changing the call to `createColumnDef` in `db-migrate-base`, but I'm hesitant to fix it there as other adapters don't seem to be having the issue.