add nonreentrant to supplyTokenTo and redeemToken function

contracts/SushiYieldSource.sol

@@ -4,13 +4,14 @@ pragma solidity 0.6.12;
 
 import { IYieldSource } from "@pooltogether/yield-source-interface/contracts/IYieldSource.sol";
 import "@openzeppelin/contracts/math/SafeMath.sol";
+import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
 
 import "./ISushiBar.sol";
 import "./ISushi.sol";
 
 /// @title A pooltogether yield source for sushi token
 /// @author Steffel Fenix
-contract SushiYieldSource is IYieldSource {
+contract SushiYieldSource is IYieldSource, ReentrancyGuard {
 
     using SafeMath for uint256;
 
@@ -44,7 +45,7 @@ contract SushiYieldSource is IYieldSource {
     /// @notice Allows assets to be supplied on other user's behalf using the `to` param.
     /// @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 {
+    function supplyTokenTo(uint256 amount, address to) public override nonReentrant {
         sushiAddr.transferFrom(msg.sender, address(this), amount);
         sushiAddr.approve(address(sushiBar), amount);
 
@@ -63,7 +64,7 @@ contract SushiYieldSource is IYieldSource {
     /// @param amount The amount of `token()` to withdraw.  Denominated in `token()` as above.
     /// @dev The maxiumum that can be called for token() is calculated by balanceOfToken() above.
     /// @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) {
+    function redeemToken(uint256 amount) public override nonReentrant returns (uint256) {
         ISushiBar bar = sushiBar;
         ISushi sushi = sushiAddr;