adds touch to debates on tag destroy

spec/lib/cache_spec.rb

@@ -0,0 +1,14 @@
+require 'rails_helper'
+
+describe 'Cache flow' do
+
+  describe 'Tag destroy' do
+    it 'invalidates Debate cache keys' do
+      debate = create(:debate, tag_list: "Good, Bad")
+      tag = ActsAsTaggableOn::Tag.find_by(name: "Bad")
+
+      expect{tag.destroy}.to change {debate.reload.cache_key}
+    end
+  end
+
+end