fix(starters): update gatsby monorepo (#11938)

This PR contains the following updates:

| Package | Type | Update | Change | References |
|---|---|---|---|---|
| gatsby | dependencies | patch | `^2.1.10` -> `^2.1.11` | [source](https://togithub.com/gatsbyjs/gatsby) |
| gatsby-source-filesystem | dependencies | patch | `^2.0.20` -> `^2.0.21` | [source](https://togithub.com/gatsbyjs/gatsby) |

---

### Release Notes

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

### [`v2.1.11`](https://togithub.com/gatsbyjs/gatsby/compare/dbd71c33ced0829c5f4bc552127ef80b4a7398a5...59daee4877799bf67c3f8092b2f89e4ad541a3d1)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.10...gatsby@2.1.11)

</details>

---

### Renovate configuration

📅 **Schedule**: At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

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

👻 **Immortal**: This PR will be recreated if closed unmerged. Get [config help](https://togithub.com/renovatebot/config-help/issues) if that's undesired.

---

 - [ ] <!-- renovate-rebase -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://togithub.com/marketplace/renovate). View repository job log [here](https://renovatebot.com/dashboard#gatsbyjs/gatsby).

package.json

@@ -12,7 +12,7 @@
     "test": "echo \"Write tests! -> https://gatsby.app/unit-testing\""
   },
   "dependencies": {
-    "gatsby": "^2.1.10",
+    "gatsby": "^2.1.11",
     "react": "^16.8.2",
     "react-dom": "^16.8.2"
   },