feat(ERC20Mintable): add onlyOwner to mint and burn

contracts/test/ERC20Mintable.sol

@@ -3,15 +3,19 @@
 pragma solidity 0.8.6;
 
 import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+import "@pooltogether/owner-manager-contracts/contracts/Ownable.sol";
 
 /**
  * @dev Extension of {ERC20} that adds a set of accounts with the {MinterRole},
  * which have permission to mint (create) new tokens as they see fit.
  *
  * At construction, the deployer of the contract is the only minter.
  */
-contract ERC20Mintable is ERC20 {
-    constructor(string memory _name, string memory _symbol) ERC20(_name, _symbol) {}
+contract ERC20Mintable is ERC20, Ownable {
+    constructor(string memory _name, string memory _symbol)
+        ERC20(_name, _symbol)
+        Ownable(msg.sender)
+    {}
 
     /**
      * @dev See {ERC20-_mint}.
@@ -20,11 +24,11 @@ contract ERC20Mintable is ERC20 {
      *
      * - the caller must have the {MinterRole}.
      */
-    function mint(address account, uint256 amount) public {
+    function mint(address account, uint256 amount) public onlyOwner {
         _mint(account, amount);
     }
 
-    function burn(address account, uint256 amount) public returns (bool) {
+    function burn(address account, uint256 amount) public onlyOwner returns (bool) {
         _burn(account, amount);
         return true;
     }