add sifchain api

src/chains/mainnet/ixo.json

@@ -1,6 +1,6 @@
 {
     "chain_name": "ixo",
-    "api": ["https://impacthub.ixo.world/rest"],
+    "api": ["https://impacthub.ixo.world/rest", "https://proxies.sifchain.finance/api/impacthub-3/rest"],
     "sdk_version": "0.42.6",
     "coin_type": "118",
     "min_tx_fee": "3000",