fix idvm interface

contracts/DODOVendingMachine/impl/DVM.sol

@@ -91,6 +91,6 @@ contract DVM is DVMTrader, DVMFunding {
     // ============ Version Control ============
     
     function version() external pure returns (string memory) {
-        return "DVM 1.0.1";
+        return "DVM 1.0.2";
     }
 }

contracts/DODOVendingMachine/impl/DVMVault.sol

@@ -180,6 +180,7 @@ contract DVMVault is DVMStorage {
     }
 
     function _mint(address user, uint256 value) internal {
+        require(value > 0, "MINT_INVALID");
         _SHARES_[user] = _SHARES_[user].add(value);
         totalSupply = totalSupply.add(value);
         emit Mint(user, value);