Bump backbone from 1.2.3 to 1.3.3

Bumps [backbone](https://github.com/jashkenas/backbone) from 1.2.3 to 1.3.3.
- [Release notes](https://github.com/jashkenas/backbone/releases)
- [Commits](https://github.com/jashkenas/backbone/compare/1.2.3...1.3.3

)

Signed-off-by: dependabot[bot] <support@dependabot.com>
Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>