Update gatsby monorepo

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change	References
gatsby	dependencies	patch	2.0.28 -> 2.0.31	source
gatsby-image	dependencies	patch	2.0.15 -> 2.0.17	source
gatsby-plugin-manifest	dependencies	patch	2.0.5 -> 2.0.6	source
gatsby-plugin-netlify	dependencies	patch	2.0.1 -> 2.0.2	source
gatsby-plugin-offline	dependencies	patch	2.0.7 -> 2.0.9	source
gatsby-plugin-sharp	dependencies	patch	2.0.7 -> 2.0.8	source
gatsby-transformer-sharp	dependencies	patch	2.1.4 -> 2.1.5	source

---

Release Notes

gatsbyjs/gatsby

### [`v2.0.31`](https://renovatebot.com/gh/gatsbyjs/gatsby/compare/c80f7937b2d1729388b79eda1e3538e0e4863564...e6d7dc3a7adc122fd6a3c606978bc79dc59fce07) [Compare Source](https://renovatebot.com/gh/gatsbyjs/gatsby/compare/c80f7937b2d1729388b79eda1e3538e0e4863564...e6d7dc3a7adc122fd6a3c606978bc79dc59fce07) ### [`v2.0.30`](https://renovatebot.com/gh/gatsbyjs/gatsby/compare/e288e673949923182dc65ee05aaee506c396e8ab...c80f7937b2d1729388b79eda1e3538e0e4863564) [Compare Source](https://renovatebot.com/gh/gatsbyjs/gatsby/compare/e288e673949923182dc65ee05aaee506c396e8ab...c80f7937b2d1729388b79eda1e3538e0e4863564) ### [`v2.0.29`](https://renovatebot.com/gh/gatsbyjs/gatsby/compare/89fb257298b50bfef01634675d95a3e254ac2445...e288e673949923182dc65ee05aaee506c396e8ab) [Compare Source](https://renovatebot.com/gh/gatsbyjs/gatsby/compare/89fb257298b50bfef01634675d95a3e254ac2445...e288e673949923182dc65ee05aaee506c396e8ab)

---

Renovate configuration

:date: Schedule: "after 10pm every weekday,before 5am every weekday,every weekend" (UTC).

:vertical_traffic_light: Automerge: Enabled.

:recycle: Rebasing: Whenever PR becomes conflicted, or if you modify the PR title to begin with "rebase!".

:ghost: Immortal: This PR will be recreated if closed unmerged. Get config help if that's undesired.

---

This PR has been generated by Renovate Bot. View repository job log here.