Update dependency rollup to v2.39.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
rollup (source)	2.38.5 -> 2.39.0

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Release Notes

rollup/rollup

### [`v2.39.0`](https://togithub.com/rollup/rollup/blob/master/CHANGELOG.md#​2390) [Compare Source](https://togithub.com/rollup/rollup/compare/v2.38.5...v2.39.0) _2021-02-12_ ##### Features - Add "validate" option to verify generated chunks are valid JavaScript ([#​3952](https://togithub.com/rollup/rollup/issues/3952)) ##### Bug Fixes - Always add exports properties for uninitialized named exports ([#​3957](https://togithub.com/rollup/rollup/issues/3957)) - Allow using an external namespace reexport together with named exports ([#​3959](https://togithub.com/rollup/rollup/issues/3959)) - Avoid invalid generated code in certain scenarios with SystemJS exports ([#​3960](https://togithub.com/rollup/rollup/issues/3960)) ##### Pull Requests - [#​3952](https://togithub.com/rollup/rollup/pull/3952): implement `validate` output option and `--validate` CLI option ([@​kzc](https://togithub.com/kzc)) - [#​3956](https://togithub.com/rollup/rollup/pull/3956): Update dependencies, fix fsevents issue ([@​lukastaegert](https://togithub.com/lukastaegert)) - [#​3957](https://togithub.com/rollup/rollup/pull/3957): Make sure uninitialised exports turn up via .hasOwnProperty for non-ES formats ([@​lukastaegert](https://togithub.com/lukastaegert)) - [#​3959](https://togithub.com/rollup/rollup/pull/3959): Allow overriding individual exports of reexported external namespaces ([@​lukastaegert](https://togithub.com/lukastaegert)) - [#​3960](https://togithub.com/rollup/rollup/pull/3960): Make sure system exports are valid JavaScript ([@​lukastaegert](https://togithub.com/lukastaegert))

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