chore(deps): update dependency gatsby to v3.1.2

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
gatsby (changelog)	3.1.1 -> 3.1.2

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Release Notes

gatsbyjs/gatsby

### [`v3.1.2`](https://togithub.com/gatsbyjs/gatsby/compare/10722585e3544fd7672c6a262198461a6968b0eb...f9133d2fb4698b59a055ba4ed711303133ccdd34) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@3.1.1...gatsby@3.1.2)

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