chore(deps): update rollup to v2.7.1

[thi-bot]

This PR contains the following updates:

Package	Update	Type	Change	Sourcegraph
rollup (source)	minor	devDependencies	2.6.1 -> 2.7.1

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Release Notes

rollup/rollup

### [`v2.7.1`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​271) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.7.0...v2.7.1) _2020-04-21_ ##### Bug Fixes - Use correct path for dynamic imports if `output.paths` is used ([#​3508](https://togithub.com/rollup/rollup/issues/3508)) ##### Pull Requests - [#​3508](https://togithub.com/rollup/rollup/pull/3508): Respect output.paths in dynamic imports ([@​lukastaegert](https://togithub.com/lukastaegert)) ### [`v2.7.0`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​270) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.6.1...v2.7.0) _2020-04-21_ ##### Features - Add `preserveEntrySignatures` option to control how exports of entry points are handled ([#​3498](https://togithub.com/rollup/rollup/issues/3498)) - Add `preserveSignature` flag to `this.emitFile` to control exports of emitted chunks ([#​3498](https://togithub.com/rollup/rollup/issues/3498)) - Add `output.minifyInternalExports` option to control if internal exports are minified ([#​3498](https://togithub.com/rollup/rollup/issues/3498)) ##### Pull Requests - [#​3498](https://togithub.com/rollup/rollup/pull/3498): Add option to configure if entry signatures are preserved ([@​lukastaegert](https://togithub.com/lukastaegert))

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