Summary:
If after 5 hours there are no connected clients, shutdown the server.
This is to prevent cases whereas the long-lived instance makes users use stale versions of Flipper if Flipper stays indefinitely running in the background.
Reviewed By: passy
Differential Revision: D51111926
fbshipit-source-id: 4c38e392cf8a6a4fb840bffdea92c0b0314aefb9