comments: update to reflect golang.org/x/crypto/ssh/knownhosts change

As of the next release of the golang.org/x/crypto module, it will be possible
for golang.org/x/crypto/ssh/knownhosts to return multiple keys of the same
type for the same host, per golang/crypto#254. We
already handle that gracefully since v1.2.1 (see commit 3a35d9f), but the code
comment describing this situation needed to be updated.

Author: evanelias

knownhosts.go

@@ -194,11 +194,9 @@ func (hkdb *HostKeyDB) HostKeys(hostWithPort string) (keys []PublicKey) {
 // in the known_hosts file will properly be converted to the corresponding
 // ssh.CertAlgo* values.
 func (hkdb *HostKeyDB) HostKeyAlgorithms(hostWithPort string) (algos []string) {
-	// We ensure that algos never contains duplicates. This is done for robustness
-	// even though currently golang.org/x/crypto/ssh/knownhosts never exposes
-	// multiple keys of the same type. This way our behavior here is unaffected
-	// even if https://github.com/golang/go/issues/28870 is implemented, for
-	// example by https://github.com/golang/crypto/pull/254.
+	// We ensure that the return value never contains duplicates. This is needed
+	// since golang.org/x/crypto/ssh/knownhosts can now return multiple keys of
+	// the same type after https://github.com/golang/crypto/pull/254 was merged.
 	hostKeys := hkdb.HostKeys(hostWithPort)
 	seen := make(map[string]struct{}, len(hostKeys))
 	addAlgo := func(typ string, cert bool) {