Issue adding foreign key

[sifthedog]

Hi, I don't know if this lib is still under maintenance, but still...

Me and my teammates started using it and we were having ourselves a problem adding a new foreign key. With no error log or anything, the migration would never end.

After some debugging, we found out that the problem is with the query. It turns out it's actually generating something like this:

ALTER TABLE [dbo].[['dbo','Table']] ADD CONSTRAINT .............

Also, there is no rollback if something goes wrong. If you are still accepting new PRs, I can fix both issues for you.

[christiaanwesterbeek]

I haven't been updating this lib, but I am still using it in some of my projects with the knowledge that indeed there's no rollback. If you're willing to contribute, I can only be grateful. I will accept PR's, review, merge and publish a new version on npm in that case.

[christiaanwesterbeek]

Thanks for your contribution. Merged #6