fix: package.json & package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-ASYNC-2441827

package.json

@@ -27,7 +27,7 @@
     "jquery": "^3.5.1",
     "jquery-pjax": "~2.0",
     "js-yaml": "^3.14.0",
-    "laravel-mix": "^6.0.25",
+    "laravel-mix": "^6.0.30",
     "leaflet": "^1.3.4",
     "leaflet-ajax": "2.1.0",
     "leaflet-providers": "1.0.*",