Babel-Jest and Jest Versions Incompatible w/ React-Scripts Dependency-Requirements about re-start

[piranna]

We currently don't have tests to check version updates break things, they would be nice. Also, we are thinking to move from using templates, to convert finish-install.js in an independent CLI to just add missing platforms to current projects, that would be more flexible. Main problem with that would be web platform, but if react-native-dom gets more mature, it would be easy.

[brandongroce]

First error related to this: microsoft/react-native-windows#2003

finishInstall.js fails due to expectation of App.windows.js after react-native windows fails. Would it be better to if (existsSync('App.windows.js')) here so the install doesn't bomb out (given react-native-windows stability) or wrap it in a try catch? Or is the expectation that you would want this to fail? I can PR if this is of any interest.