fix: packages/divi-scripts/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-NODEFORGE-14114940
- https://snyk.io/vuln/SNYK-JS-NODEFORGE-14125745
- https://snyk.io/vuln/SNYK-JS-NODEFORGE-14125097

Author: snyk-bot

packages/divi-scripts/package.json

@@ -68,7 +68,7 @@
     "uglifyjs-webpack-plugin": "1.1.6",
     "url-loader": "0.6.2",
     "webpack": "3.10.0",
-    "webpack-dev-server": "2.11.0",
+    "webpack-dev-server": "4.7.3",
     "webpack-manifest-plugin": "1.3.2",
     "whatwg-fetch": "2.0.3"
   },