fix(starters): update gatsby monorepo (#13250)

This PR contains the following updates:

| Package | Type | Update | Change | References |
|---|---|---|---|---|
| gatsby | dependencies | patch | [`^2.3.15` -> `^2.3.16`](https://diff.intrinsic.com/gatsby/2.3.15/2.3.16) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-plugin-manifest | dependencies | patch | [`^2.0.27` -> `^2.0.28`](https://diff.intrinsic.com/gatsby-plugin-manifest/2.0.27/2.0.28) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-plugin-typography | dependencies | patch | [`^2.2.11` -> `^2.2.12`](https://diff.intrinsic.com/gatsby-plugin-typography/2.2.11/2.2.12) | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-remark-prismjs | dependencies | patch | [`^3.2.7` -> `^3.2.8`](https://diff.intrinsic.com/gatsby-remark-prismjs/3.2.7/3.2.8) | [source](https://togithub.com/gatsbyjs/gatsby) |

---

### Release Notes

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

### [`v2.3.16`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.3.15...gatsby@2.3.16)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.3.15...gatsby@2.3.16)

</details>

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package.json

@@ -13,7 +13,7 @@
     "test": "echo \"Write tests! -> https://gatsby.dev/unit-testing\""
   },
   "dependencies": {
-    "gatsby": "^2.3.15",
+    "gatsby": "^2.3.16",
     "react": "^16.8.6",
     "react-dom": "^16.8.6"
   },