fix solidity pragma

Author: ZumZoom

contracts/FarmingPool.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity ^0.8.9;
+pragma solidity ^0.8.0;
 
 import "@openzeppelin/contracts/access/Ownable.sol";
 import "@openzeppelin/contracts/token/ERC20/ERC20.sol";