Update DBManager.m

[FilipeMLFreitas]

download_tasks.db should be created in internal app directory (#722)

https://github.com/fluttercommunity/flutter_downloader/issues/722

[bartekpacia]

Thanks for your contribution @FilipeMLFreitas. It looks good to me, but I'm not very experienced as an iOS developer, so I'd prefer to have somebody double-check this. @Hackmodford? :)

[bartekpacia]

Sorry for the failing Action, it's my fault. I'll fix it in https://github.com/fluttercommunity/flutter_downloader/pull/729.

[Hackmodford]

I think there's a decent argument for switching. The documents directory is defined as user accessible. However, could this potentially cause issues if an update is performed while a download is in progress?

We might want to consider migrating the db file to ensure backwards compatibility.

[lyio]

@Hackmodford I agree here. But there is no database migration for iOS at all. So it's not trivial to add this here.

We'd have to look for the DB file in the new location and in the old location and move it over if it exists in the old one.

[bartekpacia]

Looks like the migration part was done in #757 by @ndelanou :)

[bartekpacia]

I fixed the conflicts.