Relax default roundtrip check interval

probes/imap/imap_roundtrip_probe.go

@@ -20,7 +20,7 @@ import (
 	"git.autistici.org/ai3/tools/service-prober/protocol/ssl"
 )
 
-var defaultCheckInterval = 5 * time.Second
+var defaultCheckInterval = 10 * time.Second
 
 type imapRoundtripProbeSpec struct {
 	DNSMap      map[string]string `json:"dns_map"`