Add support for Ruby 2.7 and its kwargs (attr-encrypted#383)

In Ruby 3.0, positional arguments and keyword arguments will be
separated. Ruby 2.7 will warn for behaviors that will change in Ruby
3.0.

Co-authored-by: Igor Drozdov <idrozdov@gitlab.com>

lib/attr_encrypted/adapters/active_record.rb

@@ -61,7 +61,7 @@ def attr_encrypted(*attrs)
             end
 
             define_method("#{attr}_changed?") do |options = {}|
-              attribute_changed?(attr, options)
+              attribute_changed?(attr, **options)
             end
 
             define_method("#{attr}_change") do