Update changelog.json

Pondering far-too-long over whether to end with a full-stop or exclamation mark.

docs/changelog.json

@@ -7,5 +7,5 @@
   "6": "Many small performance improvements & bug fixes. Enjoy!",
   "7": "Improved the look & performance of the upload/download chart.",
   "8": "Updated to Node.js v18.",
-  "9": "Fixed issue on Synology NAS, added sessionless HTTP API auth & automatic dark mode!"
+  "9": "Fixed issue on Synology NAS, added sessionless HTTP API auth & automatic dark mode."
 }