build(deps): bump gatsby-plugin-offline from 3.0.16 to 3.1.2 (#466)

Bumps [gatsby-plugin-offline](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-offline) from 3.0.16 to 3.1.2.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-offline/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-plugin-offline@3.1.2/packages/gatsby-plugin-offline)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

package.json

@@ -15,7 +15,7 @@
     "gatsby-plugin-catch-links": "^2.0.9",
     "gatsby-plugin-emotion": "^4.2.1",
     "gatsby-plugin-manifest": "^2.3.3",
-    "gatsby-plugin-offline": "^3.0.16",
+    "gatsby-plugin-offline": "^3.1.2",
     "gatsby-plugin-react-helmet": "^3.2.1",
     "gatsby-plugin-sharp": "^2.5.3",
     "gatsby-plugin-sitemap": "^2.0.5",