Refactor migrations_paths of schema spec
What does this MR do and why?
In the repository of JiHu, if the configuration of db directory is modified, the JiHu specific migration files will be saved in the jh/db/migrate directory.
In order to adapt to this case, we need to modify the default directory in this unit test:
spec/migrations/active_record/schema_spec.rbEdited by Baodong