Fixing bootstrap import (js) and old webpack config (fixes #2875)

Author: liarco

assets/js/app.js

@@ -3,7 +3,7 @@ require('../css/app.scss');
 
 global.$ = global.jQuery = require('jquery');
 
-import 'bootstrap/js/src/index.js';
+import 'bootstrap';
 
 import './adminlte.js';
 import 'jquery.are-you-sure';

package.json

@@ -1,18 +1,16 @@
 {
   "devDependencies": {
     "@fortawesome/fontawesome-free": "^5.8.1",
-    "@symfony/webpack-encore": "^0.21",
+    "@symfony/webpack-encore": "^0.27",
     "bootstrap": "^4.1.0",
     "bootstrap-rtl": "^3.3.4",
     "codemirror": "^5.47.0",
-    "cssnano": "^4.1.7",
     "featherlight": "^1.7.13",
     "jquery": "^3.3.1",
     "jquery-highlight": "^3.4.0",
     "jquery.are-you-sure": "^1.9.0",
     "node-sass": "^4.9.4",
     "popper.js": "^1.14.5",
-    "postcss-loader": "^3.0.0",
     "sass-loader": "^7.1.0",
     "select2": "4.0.5",
     "select2-bootstrap-theme": "^0.1.0-beta.10",