Update laravel mix

package.json

@@ -15,9 +15,11 @@
         "bootstrap": "^4.2.1",
         "cross-env": "^5.2.0",
         "jquery": "^3.2",
-        "laravel-mix": "^2.1.14",
         "lodash": "^4.17.11",
         "popper.js": "^1.14.6",
+        "resolve-url-loader": "^2.3.1",
+        "sass": "^1.15.2",
+        "sass-loader": "^7.1.0",
         "vue": "^2.5.21",
         "vue-template-compiler": "^2.5.21"
     },
@@ -27,9 +29,12 @@
         "filesize": "^3.6.1",
         "infinite-scroll": "^3.0.4",
         "laravel-echo": "^1.5.2",
+        "laravel-mix": "^4.0.12",
+        "node-sass": "^4.11.0",
         "opencollective": "^1.0.3",
         "opencollective-postinstall": "^2.0.1",
         "plyr": "^3.4.7",
+        "promise-polyfill": "8.1.0",
         "pusher-js": "^4.2.2",
         "readmore-js": "^2.2.1",
         "socket.io-client": "^2.2.0",