convert ERC20Capped to initializers

contracts/mocks/ERC20CappedMock.sol

@@ -0,0 +1,14 @@
+pragma solidity ^0.4.24;
+
+import "../Initializable.sol";
+import "../token/ERC20/ERC20Capped.sol";
+import "./MinterRoleMock.sol";
+
+
+contract ERC20CappedMock is Initializable, ERC20Capped, MinterRoleMock {
+
+  constructor(uint256 cap) public {
+    ERC20Capped.initialize(cap);
+  }
+
+}

contracts/token/ERC20/ERC20Capped.sol

@@ -1,5 +1,6 @@
 pragma solidity ^0.4.24;
 
+import "../../Initializable.sol";
 import "./ERC20Mintable.sol";
 
 
@@ -7,13 +8,16 @@ import "./ERC20Mintable.sol";
  * @title Capped token
  * @dev Mintable token with a token cap.
  */
-contract ERC20Capped is ERC20Mintable {
+contract ERC20Capped is Initializable, ERC20Mintable {
 
   uint256 private _cap;
 
-  constructor(uint256 cap)
+  function initialize(uint256 cap)
     public
+    initializer
   {
+    ERC20Mintable.initialize();
+
     require(cap > 0);
     _cap = cap;
   }

test/token/ERC20/ERC20Capped.test.js

@@ -3,7 +3,7 @@ const { ether } = require('../../helpers/ether');
 const { shouldBehaveLikeERC20Mintable } = require('./behaviors/ERC20Mintable.behavior');
 const { shouldBehaveLikeERC20Capped } = require('./behaviors/ERC20Capped.behavior');
 
-const ERC20Capped = artifacts.require('ERC20Capped');
+const ERC20Capped = artifacts.require('ERC20CappedMock');
 
 contract('ERC20Capped', function ([_, minter, ...otherAccounts]) {
   const cap = ether(1000);