Update to use with latest rxdart version

[nosmirck]

flutter pub get
Running "flutter pub get" in project...                   
Because rx_command >=5.0.0 depends on rxdart ^0.23.1 and project depends on rxdart ^0.24.1, rx_command >=5.0.0 is forbidden.

So, because project depends on rx_command ^5.0.3, version solving failed.
pub get failed (1; So, because project depends on rx_command ^5.0.3, version solving failed.)
exit code 1

[baku-apps]

When I bump up the rx_dart package (to 0.24) in the rx_command pub package several unit tests fail :(

[escamoteur]

Thanks for the PR! I just pushed V5.1.0