Update less requirement to ^3.8.0 in /{{cookiecutter.app_name}}

Updates the requirements on [less](https://github.com/less/less.js) to permit the latest version.
- [Release notes](https://github.com/less/less.js/releases)
- [Changelog](https://github.com/less/less.js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/less/less.js/commits/v3.8.0)

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

{{cookiecutter.app_name}}/package.json

@@ -38,7 +38,7 @@
     "extract-text-webpack-plugin": "^2.1.2",
     "file-loader": "^1.1.11",
     "font-awesome-webpack": "0.0.5-beta.2",
-    "less": "^2.7.2",
+    "less": "^3.8.0",
     "less-loader": "^4.0.4",
     "manifest-revision-webpack-plugin": "^0.4.0",
     "raw-loader": "^0.5.1",