chore(deps): update dependency rollup to v2.55.1

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
rollup (source)	2.55.0 -> 2.55.1

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Release Notes

rollup/rollup

### [`v2.55.1`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​2551) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.55.0...v2.55.1) *2021-07-29* ##### Bug Fixes - Improve CLI warning message for unused external imports ([#​4194](https://togithub.com/rollup/rollup/issues/4194)) ##### Pull Requests - [#​4194](https://togithub.com/rollup/rollup/pull/4194): Align batch warning for UNUSED_EXTERNAL_IMPORT to individual warning ([@​benmccann](https://togithub.com/benmccann))

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