Annotate should reset the cached information about columns because Annotate may output old information if we load ActiveRecord::Base class in migration files.

For example, if we have a following migration file and execute 'rake db:migrate', Annote does not output the default value and a not null constraint of the `some_value` column.

```ruby
class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.integer :some_value
    end

    # add a not null constraint to the some_value column

    # should update some_value with not null values
    # because records might exist which have null value in the some_value column

    Post.update_all(some_value: 1)

    change_column_null(:posts, :some_value, false)
    change_column_default(:posts, :some_value, 1)
  end
end
```

This commit fixes the above issue.