chore(package): update nyc to version 15.0.0

Closes #46

Author: greenkeeper[bot]

package.json

@@ -57,7 +57,7 @@
     "mocha-lcov-reporter": "1.3.0",
     "mocha-performance": "0.1.1",
     "mysql2": "1.6.2",
-    "nyc": "^12.0.1",
+    "nyc": "^15.0.0",
     "pg": "7.6.1",
     "pg-hstore": "2.3.2",
     "plato": "1.7.0",