fix: use safe math for minDripInterval

Author: pcarranzav

contracts/l2/reservoir/IL2Reservoir.sol

@@ -27,7 +27,7 @@ interface IL2Reservoir is IReservoir {
      * @param _issuanceBase Base value for token issuance (approximation for token supply times L2 rewards fraction)
      * @param _issuanceRate Rewards issuance rate, using fixed point at 1e18, and including a +1
      * @param _nonce Incrementing nonce to ensure messages are received in order
-     * @param _keeperReward Keeper reward to distribute between keeper that called drip and keeper that redeemed  the retryable tx
+     * @param _keeperReward Keeper reward to distribute between keeper that called drip and keeper that redeemed the retryable tx
      * @param _l1Keeper Address of the keeper that called drip in L1
      */
     function receiveDrip(

contracts/l2/reservoir/L2Reservoir.sol

@@ -135,7 +135,7 @@ contract L2Reservoir is L2ReservoirV2Storage, Reservoir, IL2Reservoir {
      * @param _issuanceBase Base value for token issuance (approximation for token supply times L2 rewards fraction)
      * @param _issuanceRate Rewards issuance rate, using fixed point at 1e18, and including a +1
      * @param _nonce Incrementing nonce to ensure messages are received in order
-     * @param _keeperReward Keeper reward to distribute between keeper that called drip and keeper that redeemed  the retryable tx
+     * @param _keeperReward Keeper reward to distribute between keeper that called drip and keeper that redeemed the retryable tx
      * @param _l1Keeper Address of the keeper that called drip in L1
      */
     function receiveDrip(
@@ -168,7 +168,7 @@ contract L2Reservoir is L2ReservoirV2Storage, Reservoir, IL2Reservoir {
             grt.transfer(redeemer, _l2KeeperReward);
             grt.transfer(_l1Keeper, _keeperReward.sub(_l2KeeperReward));
         } else {
-            // In an auto-redeem, we just send all the rewards to teh L1 keeper:
+            // In an auto-redeem, we just send all the rewards to the L1 keeper:
             grt.transfer(_l1Keeper, _keeperReward);
         }
 

contracts/reservoir/L1Reservoir.sol

@@ -73,6 +73,8 @@ contract L1Reservoir is L1ReservoirV2Storage, Reservoir {
      * to the drip function, that also requires the initial supply snapshot to be taken
      * using initialSnapshot. For this reason, issuanceRate and l2RewardsFraction
      * are not initialized here and instead need a call to setIssuanceRate and setL2RewardsFraction.
+     * The same applies to minDripInterval (set through setMinDripInterval) and dripRewardPerBlock
+     * (set through setDripRewardPerBlock).
      * On the other hand, the l2ReservoirAddress is not expected to be known at initialization
      * time and must therefore be set using setL2ReservoirAddress.
      * The RewardsManager's address might also not be available in the controller at initialization
@@ -292,7 +294,10 @@ contract L1Reservoir is L1ReservoirV2Storage, Reservoir {
         uint256 _l2MaxSubmissionCost,
         address _keeperRewardBeneficiary
     ) private {
-        require(block.number > lastRewardsUpdateBlock + minDripInterval, "WAIT_FOR_MIN_INTERVAL");
+        require(
+            block.number > lastRewardsUpdateBlock.add(minDripInterval),
+            "WAIT_FOR_MIN_INTERVAL"
+        );
 
         uint256 mintedRewardsTotal = getNewGlobalRewards(rewardsMintedUntilBlock);
         uint256 mintedRewardsActual = getNewGlobalRewards(block.number);