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

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-PATHTOREGEXP-7925106
- https://snyk.io/vuln/SNYK-JS-BRACES-6838727

package.json

@@ -73,7 +73,7 @@
     "eslint-plugin-json": "^2.1.1",
     "eslint-plugin-prettier": "^3.1.4",
     "eslint-plugin-react": "7.26.1",
-    "express": "^4.17.3",
+    "express": "^4.20.0",
     "fake-indexeddb": "^2.0.4",
     "front-matter": "^2.3.0",
     "fs-extra": "^9.0.1",
@@ -90,7 +90,7 @@
     "parallel-webpack": "^2.3.0",
     "prettier": "^2.6.0",
     "rimraf": "^2.5.2",
-    "sass": "^1.27.0",
+    "sass": "^1.79.0",
     "sass-loader": "^10.0.3",
     "semver": "^5.7.2",
     "split2": "^3.2.2",