Update dependency gatsby to v2.20.13

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
gatsby (changelog)	dependencies	patch	2.20.12 -> 2.20.13

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Release Notes

gatsbyjs/gatsby

### [`v2.20.13`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.20.12...gatsby@2.20.13) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.20.12...gatsby@2.20.13)

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