convert ERC20Burnable to initializers

contracts/mocks/ERC20BurnableMock.sol

 pragma solidity ^0.4.24;
 
+import "../Initializable.sol";
 import "../token/ERC20/ERC20Burnable.sol";
 
 
-contract ERC20BurnableMock is ERC20Burnable {
+contract ERC20BurnableMock is Initializable, ERC20Burnable {
 
   constructor(address initialAccount, uint256 initialBalance) public {
     _mint(initialAccount, initialBalance);

contracts/token/ERC20/ERC20Burnable.sol

 pragma solidity ^0.4.24;
 
+import "../../Initializable.sol";
 import "./ERC20.sol";
 
 
@@ -7,7 +8,7 @@ import "./ERC20.sol";
  * @title Burnable Token
  * @dev Token that can be irreversibly burned (destroyed).
  */
-contract ERC20Burnable is ERC20 {
+contract ERC20Burnable is Initializable, ERC20 {
 
   /**
    * @dev Burns a specific amount of tokens.