fix example

src/lib.rs

@@ -69,7 +69,7 @@
 //!
 //!
 //! fn main() {
-//!     let (pk, sk) = generate_key_pair(None, 3).unwrap();
+//!     let (pk, sk) = generate_keypair_768(None).unwrap();
 //!
 //!     let (ciphertext, alice_secret) = alice(pk);
 //!