Pin another dep

import_map.json

@@ -9,7 +9,7 @@
     "preact": "https://esm.sh/preact@10.13.2",
     "preact/": "https://esm.sh/preact@10.13.2/",
     "preact-render-to-string": "https://esm.sh/preact-render-to-string@6.0.2?deps=preact@10.13.2&pin=v116",
-    "showdown": "https://esm.sh/showdown@2.1.0",
+    "showdown": "https://esm.sh/showdown@2.1.0?pin=v116",
     "utils/": "./utils/"
   }
 }