previous hash added to GBT

src/rpc/core_rpc_server.cpp

@@ -475,6 +475,7 @@ namespace cryptonote
       LOG_ERROR("Failed to calculate offset for ");
       return false;
     }
+    res.prev_hash = string_tools::pod_to_hex(b.prev_id);
     res.blocktemplate_blob = string_tools::buff_to_hex_nodelimer(block_blob);
     res.status = CORE_RPC_STATUS_OK;
     return true;