convert ERC20Mintable

contracts/mocks/ERC20MintableMock.sol

 pragma solidity ^0.4.24;
 
+import "../Initializable.sol";
 import "../token/ERC20/ERC20Mintable.sol";
 import "./MinterRoleMock.sol";
 
 
-contract ERC20MintableMock is ERC20Mintable, MinterRoleMock {
+contract ERC20MintableMock is Initializable, ERC20Mintable, MinterRoleMock {
+
+  constructor() public {
+    ERC20Mintable.initialize();
+  }
+
 }

contracts/token/ERC20/ERC20Mintable.sol

 pragma solidity ^0.4.24;
 
+import "../../Initializable.sol";
 import "./ERC20.sol";
 import "../../access/roles/MinterRole.sol";
 
@@ -8,7 +9,7 @@ import "../../access/roles/MinterRole.sol";
  * @title ERC20Mintable
  * @dev ERC20 minting logic
  */
-contract ERC20Mintable is ERC20, MinterRole {
+contract ERC20Mintable is Initializable, ERC20, MinterRole {
   event MintingFinished();
 
   bool private _mintingFinished = false;
@@ -18,6 +19,10 @@ contract ERC20Mintable is ERC20, MinterRole {
     _;
   }
 
+  function initialize() public initializer {
+    MinterRole.initialize();
+  }
+
   /**
    * @return true if the minting is finished.
    */