grammar fix (#3782)

contracts/governance/TimelockController.sol

@@ -258,7 +258,7 @@ contract TimelockController is AccessControl, IERC721Receiver, IERC1155Receiver
     }
 
     /**
-     * @dev Schedule an operation that is to becomes valid after a given delay.
+     * @dev Schedule an operation that is to become valid after a given delay.
      */
     function _schedule(bytes32 id, uint256 delay) private {
         require(!isOperation(id), "TimelockController: operation already scheduled");