Fix ignoring columns from has_one association for missing_unique_indexes

[fatkodima]

class User
  has_one :account
end

class Account
end

To disable missing_unique_indexes for checking unique index on accounts.user_id, we currently should add ignore_columns: ["User(user_id)"] to the config, which does not make sense. This PR fixes that so we should write as ignore_columns: ["Account(user_id)"].