Update recommendation of JS library for merkle trees

(cherry picked from commit 8d105825e9)

contracts/utils/cryptography/MerkleProof.sol

@@ -6,16 +6,16 @@ pragma solidity ^0.8.0;
 /**
  * @dev These functions deal with verification of Merkle Tree proofs.
  *
- * The proofs can be generated using the JavaScript library
- * https://github.com/miguelmota/merkletreejs[merkletreejs].
- * Note: the hashing algorithm should be keccak256 and pair sorting should be enabled.
- *
- * See `test/utils/cryptography/MerkleProof.test.js` for some examples.
+ * The proofs can be generated using our JavaScript library
+ * https://github.com/OpenZeppelin/merkle-tree[`@openzeppelin/merkle-tree`].
+ * You will find a quickstart guide in the readme.
  *
  * WARNING: You should avoid using leaf values that are 64 bytes long prior to
  * hashing, or use a hash function other than keccak256 for hashing leaves.
  * This is because the concatenation of a sorted pair of internal nodes in
  * the merkle tree could be reinterpreted as a leaf value.
+ * OpenZeppelin's JavaScript library generates merkle trees that are safe
+ * against this attack out of the box.
  */
 library MerkleProof {
     /**