use postCss default instead of sass

package.json

@@ -14,8 +14,6 @@
         "cross-env": "^7.0",
         "laravel-mix": "^5.0.1",
         "lodash": "^4.17.13",
-        "resolve-url-loader": "^3.1.0",
-        "sass": "^1.15.2",
-        "sass-loader": "^8.0.0"
+        "resolve-url-loader": "^3.1.0"
     }
 }

resources/sass/app.scss

@@ -1 +0,0 @@
-//

webpack.mix.js

@@ -6,10 +6,12 @@ const mix = require('laravel-mix');
  |--------------------------------------------------------------------------
  |
  | Mix provides a clean, fluent API for defining some Webpack build steps
- | for your Laravel application. By default, we are compiling the Sass
+ | for your Laravel applications. By default, we are compiling the CSS
  | file for the application as well as bundling up all the JS files.
  |
  */
 
 mix.js('resources/js/app.js', 'public/js')
-    .sass('resources/sass/app.scss', 'public/css');
+    .postCss('resources/css/app.css', 'public/css', [
+        //
+    ]);