fix(starters): update dependency gatsby to ^2.0.115 (#11553)

This PR contains the following updates:

| Package | Type | Update | Change | References |
|---|---|---|---|---|
| gatsby | dependencies | patch | `^2.0.112` -> `^2.0.115` | [source](https://togithub.com/gatsbyjs/gatsby) |

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### Release Notes

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

### [`v2.0.115`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.0.114...gatsby@2.0.115)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.0.114...gatsby@2.0.115)

### [`v2.0.114`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.0.113...gatsby@2.0.114)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.0.113...gatsby@2.0.114)

### [`v2.0.113`](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.0.112...gatsby@2.0.113)

[Compare Source](https://togithub.com/gatsbyjs/gatsby/compare/gatsby@2.0.112...gatsby@2.0.113)

</details>

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---

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starters/blog/package.json

@@ -8,7 +8,7 @@
     "url": "https://github.com/gatsbyjs/gatsby/issues"
   },
   "dependencies": {
-    "gatsby": "^2.0.112",
+    "gatsby": "^2.0.115",
     "gatsby-image": "^2.0.29",
     "gatsby-plugin-feed": "^2.0.13",
     "gatsby-plugin-google-analytics": "^2.0.13",

starters/default/package.json

@@ -5,7 +5,7 @@
   "version": "0.1.0",
   "author": "Kyle Mathews <mathews.kyle@gmail.com>",
   "dependencies": {
-    "gatsby": "^2.0.112",
+    "gatsby": "^2.0.115",
     "gatsby-image": "^2.0.29",
     "gatsby-plugin-manifest": "^2.0.17",
     "gatsby-plugin-offline": "^2.0.22",