Support Ruby 2.4.

lib/pretty_text/helpers.rb

@@ -45,7 +45,7 @@ module PrettyText
     end
 
     def get_topic_info(topic_id)
-      return unless Fixnum === topic_id
+      return unless topic_id.is_a?(Integer)
       # TODO this only handles public topics, secured one do not get this
       topic = Topic.find_by(id: topic_id)
       if topic && Guardian.new.can_see?(topic)
@@ -76,4 +76,3 @@ module PrettyText
     end
   end
 end
-