Reload before checking for related EssenceNodes

The most recent version of AwesomeNestedSet stops reloading `self` when
saving. This leads to `self` having inaccurate values for `lft` and
`rgt` in our spec, making `node.self_and_descendants` sometimes not find all
children.

Luckily our specs found this.

spec/models/alchemy/node_spec.rb

@@ -143,7 +143,7 @@ module Alchemy
         let!(:parent_node) { create(:alchemy_node, children: [node]) }
 
         it "does not destroy the node and children either but adds an error" do
-          parent_node.destroy
+          parent_node.reload.destroy
           expect(parent_node).not_to be_destroyed
           expect(parent_node.errors.full_messages).to eq(["This menu item is in use inside an Alchemy element on the following pages: #{page.name}."])
         end