[battery_plus] Update dependencies

[vbuberen]

Description

Update dependencies, so the plugin won't block updates or usage of other plugins as mentioned in #648

Related Issues

Fixes #648

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

[vbuberen]

@miquelbeltran Sorry for bothering, but I believe this one is something we should take care of pretty soon.

[vbuberen]

Looks like Analyze fails for all other packages, but not battery_plus, so we should be good.

[miquelbeltran]

LGTM. I think the analysis issue is due to Flutter 2.8.0