Bump mini-css-extract-plugin from 2.4.4 to 2.7.7

Bumps [mini-css-extract-plugin](https://github.com/webpack-contrib/mini-css-extract-plugin) from 2.4.4 to 2.7.7.
- [Release notes](https://github.com/webpack-contrib/mini-css-extract-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/mini-css-extract-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/mini-css-extract-plugin@v2.4.4...v2.7.7)

---
updated-dependencies:
- dependency-name: mini-css-extract-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

package.json

@@ -47,7 +47,7 @@
     "react-slideshow-image": "^3.5.0",
     "replace": "^1.2.0",
     "showdown": "^1.9.1",
-    "mini-css-extract-plugin": "2.4.4"
+    "mini-css-extract-plugin": "2.7.7"
   },
   "devDependencies": {
     "js-string-escape": "^1.0.1",