Update dependency rollup to v1.20.3

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
rollup	devDependencies	patch	1.20.2 -> 1.20.3

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Release Notes

rollup/rollup

v1.20.3

Compare Source

2019-08-28

Bug Fixes

• Make sure file hashes change when a change of the naming pattern leads to a file name change of a dependency (#​3083)
• Fix several issues where reexporting an external "default" export could lead to invalid or incorrect code (#​3084)

Pull Requests

• #​3078: Add github actions workflow config for windows (@​shellscape)
• #​3083: Properly reflect dependency file names in hash (@​lukastaegert)
• #​3084: Fix "default" reexport issues in non ESM/System formats (@​lukastaegert)

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