Add possibility to start checks after a defined version

[giovannibenussi]

I tried to use this gem but I wasn't able because this could break migrations for other members of my team when their try to run migrations.

I ended up switching to strong_migrations because they provide support for existing migrations through the use of an initializer file in an easy way like this:

StrongMigrations.start_after = 20170101000000

I couldn't find something similar in this gem I think it would be useful to provide this kind of functionality.

[bheemreddy181-zz]

Related #39