Upgrade nyc package fo fix lodash security issue. (#218)

https://github.com/tensorflow/tfjs-node/network/alert/yarn.lock/lodash/open

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package.json

@@ -33,7 +33,7 @@
  "@types/rimraf": "~2.0.2",
  "clang-format": "~1.2.2",
  "jasmine": "~3.1.0",
- "nyc": "^12.0.2",
+ "nyc": "^13.3.0",
  "shelljs": "^0.8.3",
  "tmp": "^0.0.33",
  "ts-node": "^5.0.1",