fix(package): update nyc to version 15.1.0

Closes #180

Author: greenkeeper[bot]

package.json

@@ -35,7 +35,7 @@
     "frontmatter-loader": "0.0.1",
     "json-loader": "^0.5.4",
     "memory-fs": "^0.4.1",
-    "nyc": "^10.0.0",
+    "nyc": "^15.1.0",
     "webpack": "^2.2.0-rc.1"
   },
   "devDependencies": {