Update dependency gatsby to v2.15.8

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
gatsby	devDependencies	minor	2.13.76 -> 2.15.8

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Release Notes

gatsbyjs/gatsby

### [`v2.15.8`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.7...gatsby@2.15.8) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.7...gatsby@2.15.8) ### [`v2.15.7`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.6...gatsby@2.15.7) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.6...gatsby@2.15.7) ### [`v2.15.6`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.5...gatsby@2.15.6) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.5...gatsby@2.15.6) ### [`v2.15.5`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.4...gatsby@2.15.5) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.4...gatsby@2.15.5) ### [`v2.15.4`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.3...gatsby@2.15.4) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.3...gatsby@2.15.4) ### [`v2.15.3`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.2...gatsby@2.15.3) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.2...gatsby@2.15.3) ### [`v2.15.2`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.1...gatsby@2.15.2) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.1...gatsby@2.15.2) ### [`v2.15.1`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.0...gatsby@2.15.1) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.15.0...gatsby@2.15.1) ### [`v2.15.0`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.7...gatsby@2.15.0) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.7...gatsby@2.15.0) ### [`v2.14.7`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.6...gatsby@2.14.7) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.6...gatsby@2.14.7) ### [`v2.14.6`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.5...gatsby@2.14.6) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.5...gatsby@2.14.6) ### [`v2.14.5`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.4...gatsby@2.14.5) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.4...gatsby@2.14.5) ### [`v2.14.4`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.3...gatsby@2.14.4) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.3...gatsby@2.14.4) ### [`v2.14.3`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.2...gatsby@2.14.3) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.2...gatsby@2.14.3) ### [`v2.14.2`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.1...gatsby@2.14.2) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.1...gatsby@2.14.2) ### [`v2.14.1`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.0...gatsby@2.14.1) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.14.0...gatsby@2.14.1) ### [`v2.14.0`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.83...gatsby@2.14.0) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.83...gatsby@2.14.0) ### [`v2.13.83`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.82...gatsby@2.13.83) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.82...gatsby@2.13.83) ### [`v2.13.82`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.81...gatsby@2.13.82) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.81...gatsby@2.13.82) ### [`v2.13.81`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.80...gatsby@2.13.81) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.80...gatsby@2.13.81) ### [`v2.13.80`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.79...gatsby@2.13.80) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.79...gatsby@2.13.80) ### [`v2.13.79`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.78...gatsby@2.13.79) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.78...gatsby@2.13.79) ### [`v2.13.78`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.77...gatsby@2.13.78) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.77...gatsby@2.13.78) ### [`v2.13.77`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.76...gatsby@2.13.77) [Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.13.76...gatsby@2.13.77)

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