Fix setMetadata RPC saferphore

lib/metadata.js

@@ -144,7 +144,7 @@ var handleCommand = Meta.handleCommand = function (meta, line) {
         throw new Error("METADATA_UNSUPPORTED_COMMAND");
     }
 
-    commands[command](meta, args);
+    return commands[command](meta, args);
 };
 Meta.commands = Object.keys(commands);