Tweak "expires next" phrasing

Put the emphasis on what cert in the chain expires next, but
still make the expiration date prominent.

README.md

@@ -252,7 +252,7 @@ and `CRITICAL` age threshold values with somewhat arbitrary numbers.
 
 ```ShellSession
 .\check_cert.exe --server www.google.com --port 443 --age-critical 50 --age-warning 55
-OK: leaf cert "www.google.com" expires next on 2020-08-12 12:08:31 +0000 UTC
+OK: leaf cert "www.google.com" expires next (on 2020-08-12 12:08:31 +0000 UTC)
 
 **ERRORS**
 
@@ -363,7 +363,7 @@ CERTIFICATES | SUMMARY
 
 - OK: 2 certs found for service running on www.google.com at port 443
 - OK: Provided hostname matches discovered certificate
-- FYI: leaf cert "www.google.com" expires next on 2020-08-12 12:08:31 +0000 UTC
+- FYI: leaf cert "www.google.com" expires next (on 2020-08-12 12:08:31 +0000 UTC)
 
 ============================
 CERTIFICATES | CHAIN DETAILS
@@ -405,7 +405,7 @@ CERTIFICATES | SUMMARY
 - OK: 2 certs found for service running on www.google.com at port 443
 - OK: Provided hostname matches discovered certificate
 - WARNING: 1 certificates expiring soon
-- FYI: leaf cert "www.google.com" expires next on 2020-08-12 12:08:31 +0000 UTC
+- FYI: leaf cert "www.google.com" expires next (on 2020-08-12 12:08:31 +0000 UTC)
 
 ============================
 CERTIFICATES | CHAIN DETAILS

cmd/check_cert/main.go

@@ -266,7 +266,7 @@ func main() {
 
 	nagiosExitState.LastError = nil
 	nagiosExitState.ServiceOutput = fmt.Sprintf(
-		"%s: %s cert %q expires next on %s",
+		"%s: %s cert %q expires next (on %s)",
 		"OK",
 		certs.ChainPosition(nextCertToExpire),
 		nextCertToExpire.Subject.CommonName,

cmd/lscert/main.go

@@ -202,7 +202,7 @@ func main() {
 
 	nextCertToExpire := certs.NextToExpire(certChain)
 	fmt.Printf(
-		"- FYI: %s cert %q expires next on %s",
+		"- FYI: %s cert %q expires next (on %s)",
 		certs.ChainPosition(nextCertToExpire),
 		nextCertToExpire.Subject.CommonName,
 		nextCertToExpire.NotAfter.Format("2006-01-02 15:04:05 -0700 MST"),