Squirrel.Windows Maker requires version to be specified, whereas other makers do not

When I don't specify `version` in `package.json` (which I know is not recommended) I get:

```
An unhandled error has occurred inside Forge:
An error occured while making for target: squirrel
Cannot read properties of undefined (reading 'split')
TypeError: Cannot read properties of undefined (reading 'split')
at convertVersion (D:\a\taxonium\taxonium\taxonium_electron\node_modules\electron-winstaller\lib\index.js:56:25)
```

whereas other platforms don't give this error. This inconsistency seems undesirable.

~I believe this might be fixed by something like: https://github.com/electron/windows-installer/compare/master...theosanderson:windows-installer:patch-1?expand=1~ [ed: there is also at least some downstream usage]