crypto/pbkdf2: fix code example for Key

The type for password is not `[]byte` (as it was in golang.org/x/crypto/pbkdf2), it is `string`.

Change-Id: I914a81a500a6d93f994b587814f26285aef7b96d
GitHub-Last-Rev: 5ec752e
GitHub-Pull-Request: #72746
Reviewed-on: https://go-review.googlesource.com/c/go/+/656115
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>
Reviewed-by: Daniel McCarney <[email protected]>
Reviewed-by: Sean Liao <[email protected]>
Auto-Submit: Sean Liao <[email protected]>

Author: Gusted

src/crypto/pbkdf2/pbkdf2.go

@@ -27,7 +27,7 @@ import (
 // can get a derived key for e.g. AES-256 (which needs a 32-byte key) by
 // doing:
 //
-//	dk := pbkdf2.Key(sha1.New, []byte("some password"), salt, 4096, 32)
+//	dk := pbkdf2.Key(sha1.New, "some password", salt, 4096, 32)
 //
 // Remember to get a good random salt. At least 8 bytes is recommended by the
 // RFC.