Update extract-text-webpack-plugin requirement to ^3.0.2 in /{{cookie…

…cutter.app_name}}

Updates the requirements on [extract-text-webpack-plugin](https://github.com/webpack-contrib/extract-text-webpack-plugin) to permit the latest version.
- [Release notes](https://github.com/webpack-contrib/extract-text-webpack-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/extract-text-webpack-plugin/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack-contrib/extract-text-webpack-plugin/commits/v3.0.2)

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

{{cookiecutter.app_name}}/package.json

@@ -35,7 +35,7 @@
     "eslint": "^5.3.0",
     "eslint-config-airbnb-base": "^11.2.0",
     "eslint-plugin-import": "^2.3.0",
-    "extract-text-webpack-plugin": "^2.1.2",
+    "extract-text-webpack-plugin": "^3.0.2",
     "file-loader": "^1.1.11",
     "font-awesome-webpack": "0.0.5-beta.2",
     "less": "^3.8.0",