update: don't restart the server

The server is typically started using `overmind start`: better to
handle the update and the startup separately.

bin/update

@@ -24,6 +24,6 @@ chdir APP_ROOT do
   puts "\n== Removing old logs =="
   system! 'bin/rails log:clear'
 
-  puts "\n== Restarting application server =="
-  system! 'bin/rails restart'
+  puts "\n== Done =="
+  puts "You can now start (or restart) the application server with `overmind start`."
 end