update to support SafeERC20

contracts/SushiYieldSource.sol

@@ -1,25 +1,25 @@
 // SPDX-License-Identifier: GPL-3.0
 
 pragma solidity 0.6.12;
-
 import { IYieldSource } from "@pooltogether/yield-source-interface/contracts/IYieldSource.sol";
+import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
 import "@openzeppelin/contracts/math/SafeMath.sol";
 
 import "./ISushiBar.sol";
-import "./ISushi.sol";
 
 /// @title A pooltogether yield source for sushi token
 /// @author Steffel Fenix
 contract SushiYieldSource is IYieldSource {
-
+    using SafeERC20 for IERC20;
     using SafeMath for uint256;
 
     ISushiBar public immutable sushiBar;
-    ISushi public immutable sushiAddr;
+    IERC20 public immutable sushiAddr;
 
     mapping(address => uint256) public balances;
 
-    constructor(ISushiBar _sushiBar, ISushi _sushiAddr) public {
+    constructor(ISushiBar _sushiBar, IERC20 _sushiAddr) public {
         sushiBar = _sushiBar;
         sushiAddr = _sushiAddr;
     }
@@ -45,7 +45,7 @@ contract SushiYieldSource is IYieldSource {
     /// @param amount The amount of `token()` to be supplied
     /// @param to The user whose balance will receive the tokens
     function supplyTokenTo(uint256 amount, address to) public override {
-        sushiAddr.transferFrom(msg.sender, address(this), amount);
+        sushiAddr.safeTransferFrom(msg.sender, address(this), amount);
         sushiAddr.approve(address(sushiBar), amount);
 
         ISushiBar bar = sushiBar;
@@ -65,8 +65,8 @@ contract SushiYieldSource is IYieldSource {
     /// @return The actual amount of tokens that were redeemed. This may be different from the amount passed due to the fractional math involved. 
     function redeemToken(uint256 amount) public override returns (uint256) {
         ISushiBar bar = sushiBar;
-        ISushi sushi = sushiAddr;
-
+        IERC20 sushi = sushiAddr;
+        
         uint256 totalShares = bar.totalSupply();
         if(totalShares == 0) return 0; 
 
@@ -86,7 +86,7 @@ contract SushiYieldSource is IYieldSource {
         uint256 sushiBalanceDiff = sushiAfterBalance.sub(sushiBeforeBalance);
 
         balances[msg.sender] = balances[msg.sender].sub(requiredSharesBalance);
-        sushi.transfer(msg.sender, sushiBalanceDiff);
+        sushi.safeTransfer(msg.sender, sushiBalanceDiff);
 
         return (sushiBalanceDiff);
     }