Fix FTX crypto exchange enum name

Author: Petersoj

schema_json/endpoint/market_data/crypto/common/enums/exchange.json

@@ -3,7 +3,7 @@
   "title": "See <a href=\"https://alpaca.markets/docs/api-documentation/api-v2/market-data/alpaca-crypto-data/\">Crypto Data</a>.",
   "enum": [
     "ERSX",
-    "FTX",
+    "FTXU",
     "CBSE"
   ],
   "javaEnums": [