fix(serve): Ctrl-c works
fix(serve): Ctrl-c works

The previous server would error out on ctrl-c.  Actix doesn't.  This
would cause the `serve` thread to end while the `watch` thread would
keep going.  Really, we should always
hard-exit.

cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs