crypto/tls: fix comment typo.

This was pointed out in https://go-review.googlesource.com/#/c/27315/1
but I changed and uploaded the wrong branch. This actually makes the
fix.

Change-Id: Ib615b06c9141b914648b6abbeeb688c5ffa0d2e3
Reviewed-on: https://go-review.googlesource.com/27360Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/crypto/tls/cipher_suites.go

@@ -134,8 +134,8 @@ func macSHA1(version uint16, key []byte) macFunction {
 	return tls10MAC{hmac.New(sha1.New, key)}
 }
 
-// macSHA1 returns a SHA-256 based MAC. These are only supported in TLS 1.2 so
-// the given version is ignored.
+// macSHA256 returns a SHA-256 based MAC. These are only supported in TLS 1.2
+// so the given version is ignored.
 func macSHA256(version uint16, key []byte) macFunction {
 	return tls10MAC{hmac.New(sha256.New, key)}
 }