chore(deps): update dependency stylus to ~0.64.0

Author: renovate[bot]

Diff for: package.json

@@ -34,7 +34,7 @@
     "markdown-to-html-cli": "~4.0.0",
     "sitemap-generator": "~8.5.1",
     "sqlite3": "5.1.5",
-    "stylus": "~0.63.0",
+    "stylus": "~0.64.0",
     "uglify-js": "~3.19.0"
   },
   "engines": {