Bump @babel/polyfill from 7.10.1 to 7.12.1

Bumps [@babel/polyfill](https://github.com/babel/babel/tree/HEAD/packages/babel-polyfill) from 7.10.1 to 7.12.1.
- [Release notes](https://github.com/babel/babel/releases)
- [Commits](https://github.com/babel/babel/commits/v7.12.1/packages/babel-polyfill)

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