fix(starters): update gatsby monorepo (#12524)

This PR contains the following updates:

| Package | Type | Update | Change | References |
|---|---|---|---|---|
| gatsby | dependencies | patch | [`^2.1.30` -> `^2.1.31`](https://diff.intrinsic.com/gatsby/2.1.30/2.1.31) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-image | dependencies | patch | [`^2.0.32` -> `^2.0.33`](https://diff.intrinsic.com/gatsby-image/2.0.32/2.0.33) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-plugin-manifest | dependencies | patch | [`^2.0.23` -> `^2.0.24`](https://diff.intrinsic.com/gatsby-plugin-manifest/2.0.23/2.0.24) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-plugin-sharp | dependencies | patch | [`^2.0.27` -> `^2.0.28`](https://diff.intrinsic.com/gatsby-plugin-sharp/2.0.27/2.0.28) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-transformer-sharp | dependencies | patch | [`^2.1.16` -> `^2.1.17`](https://diff.intrinsic.com/gatsby-transformer-sharp/2.1.16/2.1.17) | [source](https://togithub.com/gatsbyjs/gatsby) |

---

### Release Notes

<details>
<summary>gatsbyjs/gatsby</summary>

### [`v2.1.31`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.30...gatsby@2.1.31)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.30...gatsby@2.1.31)

</details>

---

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package.json

@@ -13,7 +13,7 @@
     "test": "echo \"Write tests! -> https://gatsby.dev/unit-testing\""
   },
   "dependencies": {
-    "gatsby": "^2.1.30",
+    "gatsby": "^2.1.31",
     "react": "^16.8.4",
     "react-dom": "^16.8.4"
   },