Minor improvements

- Update RuboCop config
- Remove conditional check on `ActiveModel::Dirty.changes_applied`,
  since this method has been added in AM 4.1.0 and the minimum required
  AM version is 7.0

Ref:
- https://github.com/rails/rails/blob/v4.1.8/activemodel/CHANGELOG.md#rails-410-april-8-2014

Author: tagliala

.rubocop.yml

@@ -23,6 +23,9 @@ AllCops:
 Layout/LineLength:
   Enabled: false
 
+Naming/PredicateMethod:
+  AllowBangMethods: true
+
 Rails/Delegate:
   Enabled: false
 

.rubocop_todo.yml

@@ -46,18 +46,10 @@ def write_attribute(name, value)
         super
       end
 
-      if ActiveModel::Dirty.instance_methods.include?(:changes_applied)
-        def save!
-          persist!
-          changes_applied
-          true
-        end
-      else
-        def save!
-          persist!
-          @changed_attributes&.clear
-          true
-        end
+      def save!
+        persist!
+        changes_applied
+        true
       end
 
       def save