fix(starters): update dependency gatsby to ^2.1.2 (#11768)

This PR contains the following updates:

| Package | Type | Update | Change | References |
|---|---|---|---|---|
| gatsby | dependencies | patch | `^2.1.0` -> `^2.1.2` | [source](https://togithub.com/gatsbyjs/gatsby) |

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### Release Notes

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

### [`v2.1.2`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.1...gatsby@2.1.2)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.1...gatsby@2.1.2)

### [`v2.1.1`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.0...gatsby@2.1.1)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.1.0...gatsby@2.1.1)

</details>

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