transform MinterRole to initializers

contracts/access/roles/MinterRole.sol

 pragma solidity ^0.4.24;
 
+import "../../Initializable.sol";
 import "../Roles.sol";
 
 
-contract MinterRole {
+contract MinterRole is Initializable {
   using Roles for Roles.Role;
 
   event MinterAdded(address indexed account);
@@ -11,7 +12,7 @@ contract MinterRole {
 
   Roles.Role private minters;
 
-  constructor() public {
+  function initialize() public initializer {
     minters.add(msg.sender);
   }
 

contracts/mocks/MinterRoleMock.sol

@@ -4,6 +4,10 @@ import "../access/roles/MinterRole.sol";
 
 
 contract MinterRoleMock is MinterRole {
+  constructor() {
+    initialize();
+  }
+
   function removeMinter(address account) public {
     _removeMinter(account);
   }