Support for default procs

[atomical]

The column :default can be a Proc. This supports the new syntax.

Relevant issues:
#28
SchemaPlus/schema_validations#71

[coveralls]

Coverage: 99.553% (-0.4%) from 100.0% when pulling 3a5356a on atomical:support_for_default_procs into 7dcbc33 on SchemaPlus:master.

[atomical]

I'm looking for when this was changed in AR. I think I should add an AR version check to my conditional. Thoughts?

[atomical]

I found the commit.

rails/rails@744552f

ActiveRecord::Base.connection.version >= '5.6.0'

[atomical]

I guess we could use the Rails version >= v5.0.0.beta2.

[ronen]

@atomical Thanks for working on this

Looking at the "Coverage decreased" error, I see that your new code isn't being tested.

Can you add a test case to the test suite to verify that your code works as expected?