feat: Change HashMap to ConcurrentMap

Author: wardseptember

trpc-core/src/main/java/com/tencent/trpc/core/common/config/ClientConfig.java

@@ -75,7 +75,7 @@ public class ClientConfig extends BaseProtocolConfig {
     /**
      * BackendConfig mapping.
      */
-    protected Map<String, BackendConfig> backendConfigMap = Maps.newHashMap();
+    protected Map<String, BackendConfig> backendConfigMap = Maps.newConcurrentMap();
 
     /**
      * Whether the service is registered.