chore(package): update nyc to version 15.1.0

Closes #9

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
     "coveralls": "^3.0.1",
     "documentation": "^8.0.0",
     "minimist": "^1.2.0",
-    "nyc": "^12.0.1",
+    "nyc": "^15.1.0",
     "standard": "^11.0.1",
     "tape": "^4.9.0",
     "wabt": "^1.0.0"