changed the firm of changes_from_zero_to_string?

delete *column* because is unused by the method.

activerecord/lib/active_record/attribute_methods/dirty.rb

@@ -78,7 +78,7 @@ def update(*)
       def _field_changed?(attr, old, value)
         if column = column_for_attribute(attr)
           if column.number? && (changes_from_nil_to_empty_string?(column, old, value) ||
-                                changes_from_zero_to_string?(column, old, value))
+                                changes_from_zero_to_string?(old, value))
             value = nil
           else
             value = column.type_cast(value)
@@ -96,7 +96,7 @@ def changes_from_nil_to_empty_string?(column, old, value)
         column.null && (old.nil? || old == 0) && value.blank?
       end
 
-      def changes_from_zero_to_string?(column, old, value)
+      def changes_from_zero_to_string?(old, value)
         # For columns with old 0 and value non-empty string
         old == 0 && value.present? && value != '0'
       end