ENABLE_AUTO_RESTART cannot be enabled after start

[limitusus]

@kazuho I noticed current daemon does not use the new value of ENABLE_AUTO_RESTART that is updated (or newly added) online. This is because $ENV{ENABLE_AUTO_RESTART} is localed (https://github.com/kazuho/p5-Server-Starter/blob/master/lib/Server/Starter.pm#L339) but it is used outside the localized scope (https://github.com/kazuho/p5-Server-Starter/blob/master/lib/Server/Starter.pm#L300).

I'm thinking of sending you a patch when I can make time for fix but I inform you it in advance.