fix(migrators/goose): read from filesytem if no FS

[dmksnnk]

This CR should allow to read migrations folder from parent directory like ../migrations.

I have a migrations directory in the root of the project, so to make migrations work, I need to provide FS with root directory:

root, err := filepath.Abs("../../../..")
if err != nil {
  t.Fatal("get abs path", err)
}

migrator := goosemigrator.New("migrations", goosemigrator.WithFS(os.DirFS(root)))

This CR should allow to do just:

migrator := goosemigrator.New("../../../../migrations")

Also, golangmigrator does not have fs.FS by default too.

[peterldowns]

Seems reasonable! I think the tests can be simplified, so doing that in this PR #33

[peterldowns]

@dmksnnk ah you know what, the nil FS seems to cause a panic inside goose. If you can get the tests passing, and update the tests to look more like what I tried in #33 (one case with migrations, one case with ../goosemigrator/migrations, same logic copy-pasted between them instead of extracting a function and using os.chdir) I'd be willing to merge.

[dmksnnk]

Hi @peterldowns, should be fixed, please take a look 🙂

[peterldowns]

lgtm, thanks!

[peterldowns]

I'll tag a release later today. Thanks for the contribution @dmksnnk :)