Bump degenerator and nightwatch

Removes [degenerator](https://github.com/TooTallNate/node-degenerator). It's no longer used after updating ancestor dependency [nightwatch](https://github.com/nightwatchjs/nightwatch). These dependencies need to be updated together.


Removes `degenerator`

Updates `nightwatch` from 0.9.19 to 2.3.9
- [Release notes](https://github.com/nightwatchjs/nightwatch/releases)
- [Commits](nightwatchjs/nightwatch@v0.9.19...v2.3.9)

---
updated-dependencies:
- dependency-name: degenerator
  dependency-type: indirect
- dependency-name: nightwatch
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -79,7 +79,7 @@
     "karma-webpack": "^2.0.9",
     "lolex": "^2.3.1",
     "mocha": "^4.0.1",
-    "nightwatch": "^0.9.19",
+    "nightwatch": "^2.3.9",
     "node-sass": "^4.7.2",
     "opn": "^5.2.0",
     "optimize-css-assets-webpack-plugin": "^3.2.0",