remove any default enabled sites for nginx

contrib/dokku-installer.rb

@@ -16,6 +16,7 @@ if ARGV[0] == "onboot"
   		f.puts "	}"
 		f.puts "}"
 	end
+	`rm /etc/nginx/sites-enabled/*`
 	puts "Installed Upstart service and default Nginx virtualhost for installer to run on boot."
 	exit
 end