jhipster generate-blueprint broken for sub-generators (ex: client:i18n)

When I run
```
jhipster generate-blueprint --sub-generators client:i18n
```

the extended class should be 
```
import I18NGenerator from 'generator-jhipster/generators/client/generators/i18n';
```
instead of 
```
import ClientI18NGenerator from 'generator-jhipster/generators/client:i18n';
```
