Fix for undefined method `version_comments=' for #<KbArticle::Version:...>

This fixes #247 and #255. The issue boiled down to a missing column. Unfortunately, this took WAAY too long to get around to fixing.

Author: alexbevi

db/migrate/20141215120000_add_article_versions_comments.rb

@@ -0,0 +1,5 @@
+class AddArticleVersionsComments < ActiveRecord::Migration
+  def self.up
+    add_column :kb_article_versions, :version_comments, :string, limit: 255, default: "" unless column_exists?(:kb_article_versions, :version_comments)
+  end
+end