Rails 4.0 fix

The gem fails on Rails 4.0 due to the delegate method in ActiveSupport 4.0.0
Thus, in `lib/schema_validations/active_record/validations.rb` #6
```RUBY
base.delegate :load_schema_validations, :to => 'self.class'
```
will raise the error about calling private methods, since `load_schema_validations` is a private method

The bug fix just replaces the statement with `define_method`.