convert ConditionalEscrow to initializers

contracts/mocks/ConditionalEscrowMock.sol

 pragma solidity ^0.4.24;
 
 
+import "../Initializable.sol";
 import "../payment/ConditionalEscrow.sol";
 
 
 // mock class using ConditionalEscrow
-contract ConditionalEscrowMock is ConditionalEscrow {
+contract ConditionalEscrowMock is Initializable, ConditionalEscrow {
   mapping(address => bool) private _allowed;
 
+  constructor() public {
+    ConditionalEscrow.initialize();
+  }
+
   function setAllowed(address payee, bool allowed) public {
     _allowed[payee] = allowed;
   }

contracts/payment/ConditionalEscrow.sol

 pragma solidity ^0.4.24;
 
+import "../Initializable.sol";
 import "./Escrow.sol";
 
 
@@ -7,7 +8,11 @@ import "./Escrow.sol";
  * @title ConditionalEscrow
  * @dev Base abstract escrow to only allow withdrawal if a condition is met.
  */
-contract ConditionalEscrow is Escrow {
+contract ConditionalEscrow is Initializable, Escrow {
+  function initialize() public initializer {
+    Escrow.initialize();
+  }
+
   /**
   * @dev Returns whether an address is allowed to withdraw their funds. To be
   * implemented by derived contracts.