Upgrade jest to v24.0.0-alpha.2

Summary:
This diff updates all `xplat/js` to use the latest version of `jest`.

This version provides performance improvements and fixes to make some tests less flaky

Reviewed By: mjesun

Differential Revision: D10466639

fbshipit-source-id: faa769dac1475c61e00bcd76ed30760b176a2898

package.json

@@ -218,7 +218,7 @@
     "eslint-plugin-react": "7.8.2",
     "eslint-plugin-react-native": "3.5.0",
     "flow-bin": "^0.84.0",
-    "jest": "23.4.1",
+    "jest": "24.0.0-alpha.2",
     "jest-junit": "5.1.0",
     "prettier": "1.13.6",
     "react": "16.6.0-alpha.8af6728",