Change from Launchy.open to Launchy::Browser.run

lib/letter_opener/delivery_method.rb

@@ -9,7 +9,7 @@ def deliver!(mail)
       messages = mail.parts.map { |part| Message.new(location, mail, part) }
       messages << Message.new(location, mail) if messages.empty?
       messages.each { |message| message.render }
-      Launchy.open("file://#{messages.first.filepath}")
+      Launchy::Browser.run("file://#{messages.first.filepath}")
     end
   end
 end