Bump @babel/plugin-proposal-class-properties from 7.7.0 to 7.7.4

Bumps [@babel/plugin-proposal-class-properties](https://github.com/babel/babel) from 7.7.0 to 7.7.4.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.7.0...v7.7.4

)

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