⬆️ Bump gatsby from 2.18.3 to 2.18.8

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 2.18.3 to 2.18.8.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/compare/gatsby@2.18.3...gatsby@2.18.8)

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

demo/package.json

@@ -12,7 +12,7 @@
   "dependencies": {
     "@emotion/core": "^10.0.17",
     "@emotion/styled": "^10.0.23",
-    "gatsby": "^2.18.3",
+    "gatsby": "^2.18.8",
     "gatsby-plugin-emotion": "^4.1.16",
     "gatsby-plugin-google-analytics": "^2.1.29",
     "gatsby-plugin-typescript": "^2.1.19",

gatsby-theme-firebase/package.json

@@ -6,12 +6,12 @@
   "types": "index.d.ts",
   "scripts": {},
   "peerDependencies": {
-    "gatsby": "^2.18.3",
+    "gatsby": "^2.18.8",
     "react": "^16.9.0",
     "react-dom": "^16.9.0"
   },
   "devDependencies": {
-    "gatsby": "^2.18.3",
+    "gatsby": "^2.18.8",
     "react": "^16.9.0",
     "react-dom": "^16.9.0"
   },