Improve error on a botched install

[gaearon]

@kittens reported Yarn master produces a botched install with an unfriendly message like this:

(Some Google juice:)

create-react-app myapp
cd myapp
npm start

Failed to compile
Error in Unexpected token )
@ multi main

Normally I'd expect that a botched install just doesn't start so it's frustrating it starts but then produces a weird error. It would be great if we could figure out why this is happening and crash more reasonable. We might also want to find a way to surface unexpected errors like this one.

[gaearon]

Seems like no one else is hitting this so far (or at least not reporting it), and I really don't know what caused this. Closing until we have more issues like this.

[kamthamc]

@gaearon I had same issue. I tried same steps and getting the multi main error.

create-react-app myapp
cd myapp
npm start

Failed to compile
@ multi main

[gaearon]

@kamthamc Yes, it was due to Babel accidentally releasing a buggy version. It should be fine now, just delete node_modules and run npm install again. See details in #1550.