use the git releases

[ppKrauss]

Hi, ideal is to tag versions to avoid reference errors, in external projects that depends on this dataset.

At this moment, there is an error: https://goodtables.io/github/datasets/country-codes

The last Goodtables-approved version was 9b9476.... So, you can tag v1.0.0 at https://github.com/datasets/country-codes/releases as the v1.0.0@9b947645db2f47d89e131b74a2e8c0d2d11b14b4 commit-release.