Typo in doc/dnssec-guide/signing.rst

--- signing.rst.orig	2021-03-08 12:23:18.000000000 +0100
+++ signing.rst	2021-03-08 12:22:58.000000000 +0100
@@ -736,7 +736,7 @@

    dnssec-policy standard {
        dnskey-ttl 600;
-       key {
+       keys {
            ksk lifetime 365d algorithm ecdsap256sha256;
            zsk lifetime 60d algorithm ecdsap256sha256;
        };