Fix: DEPRECATION WARNING for Rails 5.1.4

[marcinwierzbicki]

As of Ruby on Rails 5.1, attribute_changed? ActiveRecord method will be deprecated.

The deprecation message:

DEPRECATION WARNING: The behavior of attribute_changed? inside of after callbacks will be changing in the next version of Rails. The new return value will reflect the behavior of calling the method after save returned (e.g. the opposite of what it returns now). To maintain the current behavior, use saved_change_to_attribute? instead.

Method saved_change_to_attribute? is recommended.

According to changes listed above I wants to rename parent_id_changed? method to saved_change_to_parent_id?.

[felixbuenemann]

Hello Marcin, thanks for you contribution!

It's not enough to just change the method, because it breaks backward-compatibility.

You need to add a check for ActiveRecord::VERSION::MAJOR >= 5 if the new methods were introduced in rails 5.0 or if they were introduced in 5.1 you also need to check for ActiveRecord::VERSION::MINOR.

[felixbuenemann]

@marcinwierzbicki I have implemented a backwards-compatible version of your changes in #68 and released gem version 2.7.0 with the fixes.