fix: fixtures/ssr2/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-BRACES-6838727
- https://snyk.io/vuln/SNYK-JS-MICROMATCH-6838728

fixtures/ssr2/package.json

@@ -20,7 +20,7 @@
     "react-error-boundary": "^3.1.3",
     "resolve": "1.12.0",
     "rimraf": "^3.0.2",
-    "webpack": "4.44.2",
+    "webpack": "5.0.0",
     "webpack-cli": "^4.2.0"
   },
   "devDependencies": {