convert Escrow to initializers

contracts/mocks/EscrowMock.sol

+pragma solidity ^0.4.24;
+
+import "../Initializable.sol";
+import "../payment/Escrow.sol";
+
+contract EscrowMock is Initializable, Escrow {
+  constructor() public {
+    Escrow.initialize();
+  }
+}

contracts/payment/Escrow.sol

 pragma solidity ^0.4.24;
 
+import "../Initializable.sol";
 import "../math/SafeMath.sol";
 import "../ownership/Secondary.sol";
 
@@ -11,7 +12,7 @@ import "../ownership/Secondary.sol";
  * should be its primary, and provide public methods redirecting to the escrow's
  * deposit and withdraw.
  */
-contract Escrow is Secondary {
+contract Escrow is Initializable, Secondary {
   using SafeMath for uint256;
 
   event Deposited(address indexed payee, uint256 weiAmount);
@@ -19,6 +20,10 @@ contract Escrow is Secondary {
 
   mapping(address => uint256) private _deposits;
 
+  function initialize() public initializer {
+    Secondary.initialize();
+  }
+
   function depositsOf(address payee) public view returns (uint256) {
     return _deposits[payee];
   }

test/payment/Escrow.test.js

 const { shouldBehaveLikeEscrow } = require('./Escrow.behavior');
 
-const Escrow = artifacts.require('Escrow');
+const Escrow = artifacts.require('EscrowMock');
 
 contract('Escrow', function ([_, primary, ...otherAccounts]) {
   beforeEach(async function () {