[fix] use newer @typechain/hardhat module

[montyanderson]

Running yarn and then yarn test led to this behavior for me:

$ hardhat test
Creating Typechain artifacts in directory typechain for target ethers-v5
Successfully generated Typechain artifacts!
An unexpected error occurred:

test/AuctionHouse.test.ts:6:64 - error TS2307: Cannot find module '../typechain' or its corresponding type declarations.

6 import { AuctionHouse, BadBidder, TestERC721, BadERC721 } from "../typechain";
                                                                 ~~~~~~~~~~~~~~

error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

After a quick google search it led me to the issue dethcrypto/TypeChain#409 which suggests using this module. It now builds and passes all tests.