Hardhat v2.8.4

This is a small patch version that improves the sample project and replaces a deprecated dependency.

Changelog

• The sample projects now include an empty .prettierc to make IDEs auto-formatting work properly in some scenarios.
• Replace deprecated eth-sig-util with @metamask/eth-sig-util (Thanks @frangio!)
• Upgraded the version of @nomiclabs/hardhat-etherscan used by the sample projects (#2217)