yarn shim requires internet access

[rwjblue]

Steps to reproduce:

1. install from source
2. notion install node
3. notion install yarn
4. turn off internet (disable wifi / unplug ethernet / etc)
5. yarn --version

You will see the following error:

❯ yarn run foo
Notion error: Could not fetch public registry
https://github.com/notion-cli/yarn-releases/raw/master/index.json: failed to lookup address information: nodename nor servname provided, or not known

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This issue was introduced sometime between v0.1.4 and ee62f75 (full compare view here). I could probably bisect further to find the specific commit, if thats helpful...

[rwjblue]

Closed by #203