Prefer Model.reflections over private Model#_reflections.

- `_reflections` returns different key type per Rails version

lib/avo/base_resource.rb

@@ -114,7 +114,7 @@ def order_actions
       end
 
       def get_record_associations(record)
-        record._reflections
+        record.class.reflections
       end
 
       def valid_association_name(record, association_name)
@@ -382,7 +382,7 @@ def hydrate_model_with_default_values
 
           if field.type == "belongs_to"
 
-            reflection = @model._reflections[@params[:via_relation]]
+            reflection = @model.class.reflections[@params[:via_relation]]
 
             if field.polymorphic_as.present? && field.types.map(&:to_s).include?(@params[:via_relation_class])
               # set the value to the actual record

lib/avo/fields/belongs_to_field.rb

@@ -245,10 +245,10 @@ def target_resource
 
         reflection_key = polymorphic_as || id
 
-        if @model._reflections[reflection_key.to_s].klass.present?
-          App.get_resource_by_model_name @model._reflections[reflection_key.to_s].klass.to_s
-        elsif @model._reflections[reflection_key.to_s].options[:class_name].present?
-          App.get_resource_by_model_name @model._reflections[reflection_key.to_s].options[:class_name]
+        if @model.class.reflections[reflection_key.to_s].klass.present?
+          App.get_resource_by_model_name @model.class.reflections[reflection_key.to_s].klass.to_s
+        elsif @model.class.reflections[reflection_key.to_s].options[:class_name].present?
+          App.get_resource_by_model_name @model.class.reflections[reflection_key.to_s].options[:class_name]
         else
           App.get_resource_by_name reflection_key.to_s
         end

lib/avo/fields/has_base_field.rb

@@ -59,10 +59,10 @@ def field_label
       end
 
       def target_resource
-        if @model._reflections[id.to_s].klass.present?
-          Avo::App.get_resource_by_model_name @model._reflections[id.to_s].klass.to_s
-        elsif @model._reflections[id.to_s].options[:class_name].present?
-          Avo::App.get_resource_by_model_name @model._reflections[id.to_s].options[:class_name]
+        if @model.class.reflections[id.to_s].klass.present?
+          Avo::App.get_resource_by_model_name @model.class.reflections[id.to_s].klass.to_s
+        elsif @model.class.reflections[id.to_s].options[:class_name].present?
+          Avo::App.get_resource_by_model_name @model.class.reflections[id.to_s].options[:class_name]
         else
           Avo::App.get_resource_by_name id.to_s
         end