chore(deps): update dependency optimize-css-assets-webpack-plugin to v6

Author: renovate-bot

package.json

@@ -32,7 +32,7 @@
     "css-loader": "2.1.0",
     "file-loader": "3.0.1",
     "node-sass": "4.11.0",
-    "optimize-css-assets-webpack-plugin": "5.0.1",
+    "optimize-css-assets-webpack-plugin": "6.0.0",
     "sass-loader": "7.1.0",
     "vue": "2.5.22",
     "vue-loader": "15.6.2",