[pkg] Update nyc to version 15.1.0 (#230)

Author: greenkeeper[bot]

package.json

@@ -47,7 +47,7 @@
     "assume": "~2.2.0",
     "browserify": "~16.5.0",
     "mocha": "~7.2.0",
-    "nyc": "~15.0.0",
+    "nyc": "~15.1.0",
     "pre-commit": "~1.2.0",
     "sauce-browsers": "~2.0.0",
     "sauce-test": "~1.3.3",