refactor: set lib and target to es6 in tsconfig.json

tsconfig.json

@@ -2,7 +2,7 @@
   "compilerOptions": {
     "esModuleInterop": true,
     "forceConsistentCasingInFileNames": true,
-    "lib": ["es5", "es6"],
+    "lib": ["es6"],
     "module": "commonjs",
     "moduleResolution": "node",
     "noImplicitAny": true,
@@ -10,7 +10,7 @@
     "resolveJsonModule": true,
     "sourceMap": true,
     "strict": true,
-    "target": "es5"
+    "target": "es6"
   },
   "exclude": ["artifacts", "node_modules"],
   "files": ["./hardhat.config.ts"],