chore(package): update nyc to version 15.1.0

Closes #8

Author: greenkeeper[bot]

package.json

@@ -46,7 +46,7 @@
     "eslint-plugin-react": "^7.4.0",
     "mocha": "^5.2.0",
     "mocha-lcov-reporter": "^1.3.0",
-    "nyc": "^13.1.0"
+    "nyc": "^15.1.0"
   },
   "dependencies": {
     "linear-algebra": "^3.1.4"