ldnssec-keygen.1: fixes for `mandoc -Tlint`

ldnssec-keygen.1

@@ -116,7 +116,7 @@ The following commands will define its use.
 If the generated key will be used as a
 .Em ZSK
 for the zone
-.Em zsk.example. ,
+.Ql zsk.example\&. ,
 then
 .Bd -literal -offset indent
 $ ldnssec-keygen filename -d zsk.example. <sk
@@ -138,7 +138,7 @@ ksk.example.    3600    IN      DNSKEY  256 3 13 g02jgUGsc01VjH2bUM9Dob5ulaA+BuS
 If instead the key was intended to be used as a
 .Em KSK
 for the zone
-.Em ksk.example. ,
+.Ql ksk.example\&. ,
 then
 .Bd -literal -offset indent
 $ ldnssec-keygen filename -d ksk.example. -k <sk