chore(deps): update dependency rollup to v2.26.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
rollup (source)	devDependencies	patch	2.26.0 -> 2.26.1

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Release Notes

rollup/rollup

### [`v2.26.1`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​2261) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.26.0...v2.26.1) _2020-08-16_ ##### Bug Fixes - Correctly render external namespace imports when only generating SystemJS output ([#​3731](https://togithub.com/rollup/rollup/issues/3731)) ##### Pull Requests - [#​3731](https://togithub.com/rollup/rollup/pull/3731): Render system namespace import ([@​sastan](https://togithub.com/sastan) and [@​lukastaegert](https://togithub.com/lukastaegert))

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:tada: This PR is included in version 3.3.2 :tada:

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