Mixup between UserPreferences and Preferences in chapter 6

[Tommy0304]

class UserPreferencesRepository( private val userPreferencesStore: DataStore<UserPreferences>, <-- this. should be Preferences context: Context ) { ... }

also, hard to follow. The student does not know where to insert the new code, therefore it leads to unexpected errors

[mmoczkowski]

Thank you, this is noted, fix is underway. Closing in favor of #45 which has better description.