Remove implicit ordering when searching existing row by constraint

When seed_fu is seeding, it first tries finding existing record, and this is done by a constraint:

`
City Load (1.9ms)  SELECT  "cities".* FROM "cities"  WHERE "cities"."id" = 5990  ORDER BY "cities"."id" ASC LIMIT 1
`
I think `order by` is redundant here, so I change `.first` to `.take`