Fix icon not properly defined

The icon field was left blank, which resulted in Mod Menu complaining about it not having an icon, despite the icon already being included. This pull request fixes that.

src/main/resources/fabric.mod.json

@@ -14,7 +14,7 @@
   },
 
   "license": "CC0-1.0",
-  "icon": "",
+  "icon": "assets/icon.png",
 
   "environment": "*",
   "entrypoints": {
@@ -34,4 +34,4 @@
   "suggests": {
     "flamingo": "*"
   }
-}
+}