Update fabric.mod.json (SchemaStore#5525)

* Update fabric.mod.json

Many developers use variable-names and expand them automatically by gradle. This is intentional so that you don't need to define them in multiple places. This allows the use of these, e.g. `${MY_VAR}'.

* Update fabric.mod.json

Fix validation error (Hopefully)

Author: LunaticWasTaken

src/schemas/json/fabric.mod.json

@@ -115,7 +115,7 @@
   "properties": {
     "id": {
       "type": "string",
-      "pattern": "^[a-z][a-z0-9-_]{1,63}$",
+      "pattern": "^(?:[a-z][a-z0-9-_]{1,63}|[$]\\{[a-zA-Z0-9-_]+\\})$",
       "description": "The mod identifier"
     },
     "version": {