Update dev-dependencies

Author: wooorm

package.json

@@ -37,7 +37,7 @@
   "devDependencies": {
     "browserify": "^16.0.0",
     "dtslint": "^2.0.0",
-    "nyc": "^14.0.0",
+    "nyc": "^15.0.0",
     "prettier": "^1.0.0",
     "remark": "^11.0.0",
     "remark-attr": "^0.9.0",