Add missing import for @nomiclabs/hardhat-etherscan

Author: nkuba

hardhat.config.ts

@@ -4,6 +4,7 @@ import "@keep-network/hardhat-helpers"
 import "@keep-network/hardhat-local-networks-config"
 import "@nomiclabs/hardhat-waffle"
 import "@nomiclabs/hardhat-ethers"
+import "@nomiclabs/hardhat-etherscan"
 import "hardhat-gas-reporter"
 import "hardhat-deploy"
 import "hardhat-dependency-compiler"