Update misleading information about OpenZeppelin's ECDSA library

Author: rafales

docs/units-and-global-variables.rst

@@ -231,8 +231,8 @@ Mathematical and Cryptographic Functions
     for _transaction_ signatures (see `EIP-2 <https://eips.ethereum.org/EIPS/eip-2#specification>`_), but
     the ecrecover function remained unchanged.
 
-    This is usually not a problem unless you require signatures to be unique or
-    use them to identify items. OpenZeppelin have a `ECDSA helper library <https://docs.openzeppelin.com/contracts/2.x/api/cryptography#ECDSA>`_ that you can use as a wrapper for ``ecrecover`` without this issue.
+    This is usually not a problem unless you require signatures to be unique or use them to identify items.
+    OpenZeppelin have a `ECDSA helper library <https://docs.openzeppelin.com/contracts/4.x/api/utils#ECDSA>`_ that you can use as a wrapper for ``ecrecover`` without this issue.
 
 .. note::