Upgrade nyc devDependency from ^13.1.0 to ^14.0.0 (#649)

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "hallmark": "^0.1.0",
     "level-community": "^3.0.0",
     "memdown": "^4.0.0",
-    "nyc": "^13.1.0",
+    "nyc": "^14.0.0",
     "pinkie": "^2.0.4",
     "referee": "^1.2.0",
     "safe-buffer": "^5.1.0",