Eslint: Use non flat configuration

The TypeScript Eslint version currently supported do not require the
flat configuration.

Author: widoz

.eslintrc.json

@@ -5,13 +5,14 @@
   },
   "extends": [
     "eslint:recommended",
-    "plugin:@typescript-eslint/recommended"
+    "plugin:@typescript-eslint/recommended-type-checked"
   ],
   "parser": "@typescript-eslint/parser",
   "parserOptions": {
+    "project": true,
     "ecmaVersion": "latest",
     "sourceType": "module",
-    "project": "./tsconfig.json"
+    "tsconfigRootDir": "./"
   },
   "plugins": [
     "@typescript-eslint"