Update nyc

Author: greenkeeperio-bot

package.json

@@ -29,7 +29,7 @@
   "devDependencies": {
     "browserify": "^13.0.1",
     "esmangle": "^1.0.1",
-    "nyc": "^7.0.0",
+    "nyc": "^8.4.0",
     "parse5": "^2.1.5",
     "remark-cli": "^2.1.0",
     "remark-preset-wooorm": "^1.0.0",