Doesn't seem to obey `safety_assured` blocks

[ibrahima]

Hi! First of all, thanks for making this rubocop cop! I was about to make something similar after our 2nd or 3rd incident of brief downtime caused by an unsafe migration, but then I found this and was happy to see that it just uses strong_migrations for checking the migrations.

One thing though, it doesn't seem like the linter knows to ignore migrations that are wrapped in safety_assured. Is it supposed to, or is that just not implemented? I wasn't quite sure from looking at the code, but if it's just not implemented yet I might be able to find some time to work on a PR.

Thanks again!

[ibrahima]

The thing I'm confused about is what this commit is doing: 90ff8d2

The message makes it seem like it should ignore migrations wrapped in safety_assured, but the code looks like it just ignores specific migrations from a list?