chore(deps): update dependency nyc to v15

Signed-off-by: Renovate Bot <[email protected]>

Author: renovate-bot

package.json

@@ -55,7 +55,7 @@
     "eslint": "^5.3.0",
     "mocha": "^6.0.0",
     "npm-publish-git-tag": "^3.0.0",
-    "nyc": "^13.0.0",
+    "nyc": "^15.0.0",
     "semantic-release-github": "^4.0.17"
   }
 }