Selective module resolution doesn't work with scoped packages

[s-panferov]

#4105 cc @kaylieEB

Do you want to request a feature or report a bug?
Bug

What is the current behavior?

"resolutions": {
  "@types/react": "15.0.22"
}

Result:

Couldn't find any versions for "react" that matches "15.0.22"

The error is that yarn thinks that package @types/react is a path @types/react.

What is the expected behavior?
Yarn should correctly install the dep.

The source of bug is this line. We cannot simply split by / here.

We either have to

1. Improve parsing rules to properly split scoped packages
2. Use different package separator
3. Use some kind of escaping.

Please mention your node.js, yarn and operating system version.
yarn@1.0.0-20170823.1414
node@6.11.2
osx 10.12.6

[s-panferov]

Started to work on the fix in #4243

[kaylie-alexa]

@s-panferov awesome! Thanks for working on this :) let me know if you need any help.