Build: Upgrade from which@2 to which@4

https://github.com/npm/node-which/blob/v4.0.0/CHANGELOG.md

* which 3.0: Removes support for Node 10 and 12. Requires Node 14+.
* which 4.0: Removes support for Node 14. Requires Node 16+.

Author: Krinkle

package-lock.json

@@ -28,7 +28,7 @@
     "highlight.js": "^10.7.2",
     "marked": "^4.0.0",
     "spawnback": "^1.0.1",
-    "which": "^2.0.2",
+    "which": "^4.0.0",
     "wordpress": "^1.4.1"
   },
   "scripts": {