Fix comments not expiring cache

Gemfile

@@ -78,4 +78,6 @@ gem 'rails-controller-testing'
 
 gem 'simple_captcha2', require: 'simple_captcha'
 
-gem 'uglifier'
+gem 'uglifier'
+
+gem 'dalli'

Gemfile.lock

@@ -86,6 +86,7 @@ GEM
       ruby-enum (~> 0.5)
     concurrent-ruby (1.1.5)
     crass (1.0.4)
+    dalli (2.7.11)
     docile (1.3.2)
     email_validator (2.0.1)
       activemodel
@@ -257,6 +258,7 @@ DEPENDENCIES
   carrierwave
   coderay
   commonmarker
+  dalli
   email_validator
   github-markup
   irb
@@ -284,7 +286,7 @@ DEPENDENCIES
   webpacker (~> 4.0)
 
 RUBY VERSION
-   ruby 2.6.3p62
+   ruby 2.6.4p104
 
 BUNDLED WITH
    2.0.2

app/models/comment.rb

@@ -4,11 +4,11 @@ require 'github/markup'
 class Comment < ApplicationRecord
   belongs_to :user
   belongs_to :parent, class_name: "Comment", optional: true
-  belongs_to :post
+  belongs_to :post, touch: true
   has_many :replies, class_name: "Comment", foreign_key: :parent_id
 
   def editable_by?(user)
     # Will need to consider how this should work when/if comment editing is supported
-    return self.user_id == user.id || user.admin? || self.post.blog.user_id == user.id
+    self.user_id == user.id || user.admin? || self.post.blog.user_id == user.id
   end
 end