fix: update version pragma (#54)

Signed-off-by: Vedran Bidin <[email protected]>

Author: vbidin

contracts/test/mocks/MockERC20.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: AGPL-3.0-only
-pragma solidity 0.8.7;
+pragma solidity ^0.8.7;
 
 import { ERC20 } from "../../ERC20.sol";