Update dependency ethers to v6

Author: renovate[bot]

package.json

@@ -17,7 +17,7 @@
     "@types/mocha": "^9.1.0",
     "@types/node": ">=12.0.0",
     "chai": "^4.2.0",
-    "ethers": "^5.4.7",
+    "ethers": "^6.0.0",
     "hardhat": "^2.12.5",
     "hardhat-gas-reporter": "^1.0.8",
     "solidity-coverage": "^0.8.0",