build fails after upgrading to v7 when there are widgets that use i18n with horrible error message

**Enhancement**
Package Version: 7.0.0

**Code**
in .dojorc `"locale": "en"`

**Actual behavior:**
running `npm run dev`
```
./node_modules/@dojo/webpack-contrib/cldr/bootstrap.js
Module not found: Error: Can't resolve 'cldr-data/main/en/ca-gregorian.json' in 'C:\......\node_modules\@dojo\webpack-contrib\cldr'
resolve 'cldr-data/main/en/ca-gregorian.json' in 'C:\......\node_modules\@dojo\webpack-contrib\cldr'
Parsed request is a module
```
... this goes on and on and on...

**Wanted behavior:**
After running the upgrade tool from v5 to v6 and then to v7 I would expect my app to build like before upgrading

I would like the upgrade script to check for the `locale` setting my .dojorc and install `cldr-data` if needed. And or the build tool to report back a better message informing me I'm missing a key package.