Upgrade jest to 23.4.1

Summary:
This includes jestjs/jest@8b8f5bc, which improves the watchman query to calculate the initial haste map to be much faster under Eden.

**Time to initialize Metro after resetting jest-haste-map cache (Eden checkout)**

* Before this diff: 3m14 (sometimes taking up to 15min!! after rebasing)
* With this diff: 12s (quite constant after rebasing)

(16X improvement)

**Time to initialize Metro with a warm jest-haste-map cache (Eden checkout)**

* Before this diff: 1.1s
* With this diff: 1.1s

(I haven't seen meaningful perf changes in non-eden checkouts)

Reviewed By: mjesun

Differential Revision: D8857820

fbshipit-source-id: 5ce9da04a69bd02d121a8efe65bf369c7fa1e834

package.json

@@ -213,7 +213,7 @@
     "eslint-plugin-react": "7.8.2",
     "eslint-plugin-react-native": "^3.2.1",
     "flow-bin": "^0.76.0",
-    "jest": "23.4.0",
+    "jest": "23.4.1",
     "jest-junit": "5.1.0",
     "prettier": "1.13.6",
     "react": "16.4.1",