Fix output error in listing migration
Fix https://github.com/nixsolutions/zfcore/issues/20 "If you rename the index and generate migration is not created in the down () the old key."
Merge pull request #21 from naxel/master

Fix https://github.com/nixsolutions/zfcore/issues/20 "If you rename the index and generate migration is not created in the down () the old key."