chore(deps): update dependency rollup to v2.20.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
rollup (source)	devDependencies	minor	2.19.0 -> 2.20.0

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Release Notes

rollup/rollup

### [`v2.20.0`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​2200) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.19.0...v2.20.0) _2020-07-06_ ##### Features - Support using a function to generate different chunk and asset naming patterns per chunk or asset ([#​3658](https://togithub.com/rollup/rollup/issues/3658)) - Add `referencedFiles` property to the chunk info in generateBundle to list referenced assets ([#​3661](https://togithub.com/rollup/rollup/issues/3661)) ##### Pull Requests - [#​3658](https://togithub.com/rollup/rollup/pull/3658): Add ability to use a function that returns a pattern string in all places where you could use a pattern string before ([@​frank-dspeed](https://togithub.com/frank-dspeed)) - [#​3661](https://togithub.com/rollup/rollup/pull/3661): Add referenced files to bundle ([@​lukastaegert](https://togithub.com/lukastaegert))

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