Minimum of three machines running

Maybe this will reduce the issues with requests taking so long. My assumption is
that rolling restarts are causing this when they only leave one machine running
when there's a total of only two.

fly.toml

@@ -40,7 +40,7 @@ processes = ["web"]
 force_https = true
 auto_stop_machines = "suspend"
 auto_start_machines = true
-min_machines_running = 2
+min_machines_running = 3
 [http_service.concurrency]
 type = "requests"
 soft_limit = 2