chore(deps): update dependency nyc to v15 (#96)

Author: renovate-bot

package.json

@@ -55,7 +55,7 @@
     "js-green-licenses": "^1.0.0",
     "linkinator": "^1.4.2",
     "mocha": "^7.0.0",
-    "nyc": "^14.0.0",
+    "nyc": "^15.0.0",
     "sinon": "^8.0.0",
     "source-map-support": "^0.5.12",
     "tmp": "0.1.0",