Fix typo in ERC20._mint docs (#2648)

contracts/token/ERC20/ERC20.sol

@@ -229,7 +229,7 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
      *
      * Requirements:
      *
-     * - `to` cannot be the zero address.
+     * - `account` cannot be the zero address.
      */
     function _mint(address account, uint256 amount) internal virtual {
         require(account != address(0), "ERC20: mint to the zero address");