Fixed onError callback not being set on the Flutter framework

[matux]

Description of the change

This PR fixes a serious bug where the SDK wasn't properly hooking its onError callback to the Flutter framework which would prevent exceptions originating/or being caught by the Flutter Frameworks from being reported to Rollbar.

This PR also bumps the version to 1.4.1 as this is intended as a hot-fix to be published immediately upon merge.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Maintenance
• New release

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer