chore(deps): update dependency nyc to v15

Author: renovate-bot

package.json

@@ -65,7 +65,7 @@
     "husky": "^1.3.1",
     "mocha": "^6.0.0",
     "mock-require": "^3.0.3",
-    "nyc": "^13.1.0",
+    "nyc": "^15.0.0",
     "prettier": "^1.19.1",
     "semantic-release": "^16.0.0-beta.46",
     "sinon": "^7.4.1",