Update dependency rollup to ^2.9.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
rollup (source)	devDependencies	minor	^2.8.2 -> ^2.9.1

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Release Notes

rollup/rollup

### [`v2.9.1`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​291) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.9.0...v2.9.1) _2020-05-11_ ##### Bug Fixes - Do not create unintended live-bindings or invalid reexports when reexporting global variables ([#​3550](https://togithub.com/rollup/rollup/issues/3550)) ##### Pull Requests - [#​3550](https://togithub.com/rollup/rollup/pull/3550): Track updates of globals that are exported as default ([@​lukastaegert](https://togithub.com/lukastaegert)) ### [`v2.9.0`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​290) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.8.2...v2.9.0) _2020-05-10_ ##### Features - Add ids of static and dynamic imports to `this.getModuleInfo` ([#​3542](https://togithub.com/rollup/rollup/issues/3542)) - Provide `getModuleInfo` and `getModuleIds` to `manualChunks` functions ([#​3542](https://togithub.com/rollup/rollup/issues/3542)) - Add nullish coalescing support ([#​3548](https://togithub.com/rollup/rollup/issues/3548)) - Make the rebuild delay in watch mode configurable and set the default to `0` for snappy rebuilds ([#​3502](https://togithub.com/rollup/rollup/issues/3502)) - Add `this.getModuleIds` to the plugin context as future replacement for `this.moduleIds` ([#​3542](https://togithub.com/rollup/rollup/issues/3542)) ##### Pull Requests - [#​3502](https://togithub.com/rollup/rollup/pull/3502): Configurable build delay ([@​mattdesl](https://togithub.com/mattdesl)) - [#​3542](https://togithub.com/rollup/rollup/pull/3542): Extend manualChunks API ([@​lukastaegert](https://togithub.com/lukastaegert)) - [#​3548](https://togithub.com/rollup/rollup/pull/3548): Support nullish coalescing with tree-shaking ([@​lukastaegert](https://togithub.com/lukastaegert))

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