depend on `network_info_plus: ^4.0.0`

[János Dobszai]

flutter_offline currently depends on network_info_plus: ^2.1.2, which is a really old version. Version 3 and even version 4 were released since then.

Please depend on network_info_plus: ^4.0.0.

[Angelo Cassano]

Hey @dJani97 , I opened a PR to fix this issue