chore(deps-dev): bump nyc from 14.1.1 to 15.0.0 (#157)

Bumps [nyc](https://github.com/istanbuljs/nyc) from 14.1.1 to 15.0.0.
- [Release notes](https://github.com/istanbuljs/nyc/releases)
- [Changelog](https://github.com/istanbuljs/nyc/blob/master/CHANGELOG.md)
- [Commits](istanbuljs/nyc@v14.1.1...v15.0.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -33,7 +33,7 @@
     "eslint": "^6.1.0",
     "eslint-config-hexo": "^3.0.0",
     "mocha": "^6.0.2",
-    "nyc": "^14.1.1"
+    "nyc": "^15.0.0"
   },
   "dependencies": {
     "bluebird": "^3.5.0",