Update dependency cssnano to v5.1.15 (#2238)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package-lock.json

@@ -62,7 +62,7 @@
     "babel-loader": "8.3.0",
     "browserify-transform-tools": "1.7.0",
     "css-loader": "5.2.7",
-    "cssnano": "5.1.14",
+    "cssnano": "5.1.15",
     "eliminate": "1.1.2",
     "eslint": "8.33.0",
     "eslint-plugin-mdx": "1.17.1",