x/crypto: fix typos

The typos were found by misspell tool.

Change-Id: I120740f12f7ba48330749ebf84050a7b98e01016
Reviewed-on: https://go-review.googlesource.com/24725
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

ssh/cipher_test.go

@@ -21,7 +21,7 @@ func TestDefaultCiphersExist(t *testing.T) {
 }
 
 func TestPacketCiphers(t *testing.T) {
-	// Still test aes128cbc cipher althought it's commented out.
+	// Still test aes128cbc cipher although it's commented out.
 	cipherModes[aes128cbcID] = &streamCipherMode{16, aes.BlockSize, 0, nil}
 	defer delete(cipherModes, aes128cbcID)