Update dependency nyc to v18

Author: renovate[bot]

package.json

@@ -52,7 +52,7 @@
     "eslint-plugin-prettier": "3.4.1",
     "eslint-plugin-react": "7.37.5",
     "mocha": "7.2.0",
-    "nyc": "14.1.1",
+    "nyc": "18.0.0",
     "prettier": "1.19.1",
     "sinon": "8.1.1",
     "typescript": "3.9.10"