crypto/ssh: fix typo in error message in certs.go

Fixes golang/go#23266

Change-Id: I8da14425ed69c44a7b0c56b1aa0ea951fe297608
Reviewed-on: https://go-review.googlesource.com/85595
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/ssh/certs.go b/ssh/certs.go
index 5c9fadc..cfc8ead 100644
--- a/ssh/certs.go
+++ b/ssh/certs.go
@@ -340,7 +340,7 @@
 // the signature of the certificate.
 func (c *CertChecker) CheckCert(principal string, cert *Certificate) error {
 	if c.IsRevoked != nil && c.IsRevoked(cert) {
-		return fmt.Errorf("ssh: certicate serial %d revoked", cert.Serial)
+		return fmt.Errorf("ssh: certificate serial %d revoked", cert.Serial)
 	}
 
 	for opt := range cert.CriticalOptions {