all: remove redundant words in comments and fix some typos

Change-Id: I3078492dc020770aca630e0b362df0212bd41e32
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/569156
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Nicola Murino <nicola.murino@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Nicola Murino <nicola.murino@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

ssh/example_test.go

@@ -384,7 +384,7 @@ func ExampleCertificate_SignCert() {
 	}
 	mas, err := ssh.NewSignerWithAlgorithms(signer.(ssh.AlgorithmSigner), []string{ssh.KeyAlgoRSASHA256})
 	if err != nil {
-		log.Fatal("unable to create signer with algoritms: ", err)
+		log.Fatal("unable to create signer with algorithms: ", err)
 	}
 	certificate := ssh.Certificate{
 		Key:      publicKey,