fix(starters): update gatsby monorepo (#12650)

This PR contains the following updates:

| Package | Type | Update | Change | References |
|---|---|---|---|---|
| gatsby | dependencies | minor | [`^2.1.37` -> `^2.2.1`](https://diff.intrinsic.com/gatsby/2.1.37/2.2.1) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-remark-prismjs | dependencies | patch | [`^3.2.5` -> `^3.2.6`](https://diff.intrinsic.com/gatsby-remark-prismjs/3.2.5/3.2.6) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-transformer-remark | dependencies | patch | [`^2.3.5` -> `^2.3.7`](https://diff.intrinsic.com/gatsby-transformer-remark/2.3.5/2.3.7) | [source](https://togithub.com/gatsbyjs/gatsby) |

---

### Release Notes

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

### [`v2.2.1`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.2.0...gatsby@2.2.1)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.2.0...gatsby@2.2.1)

### [`v2.2.0`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.39...gatsby@2.2.0)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.39...gatsby@2.2.0)

### [`v2.1.39`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.38...gatsby@2.1.39)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.38...gatsby@2.1.39)

### [`v2.1.38`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.37...gatsby@2.1.38)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.37...gatsby@2.1.38)

</details>

---

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package.json

@@ -13,7 +13,7 @@
     "test": "echo \"Write tests! -> https://gatsby.dev/unit-testing\""
   },
   "dependencies": {
-    "gatsby": "^2.1.37",
+    "gatsby": "^2.2.1",
     "react": "^16.8.4",
     "react-dom": "^16.8.4"
   },