update docs kafka.md (#3936)

docs/en/operations/table_engines/kafka.md

@@ -24,7 +24,7 @@ Kafka SETTINGS
   kafka_topic_list = 'topic1,topic2',
   kafka_group_name = 'group1',
   kafka_format = 'JSONEachRow',
-  kafka_row_delimiter = '\n'
+  kafka_row_delimiter = '\n',
   kafka_schema = '',
   kafka_num_consumers = 2
 ```

docs/ru/operations/table_engines/kafka.md

@@ -23,7 +23,7 @@ Kafka SETTINGS
   kafka_topic_list = 'topic1,topic2',
   kafka_group_name = 'group1',
   kafka_format = 'JSONEachRow',
-  kafka_row_delimiter = '\n'
+  kafka_row_delimiter = '\n',
   kafka_schema = '',
   kafka_num_consumers = 2
 ```

docs/zh/operations/table_engines/kafka.md

@@ -23,7 +23,7 @@ Kafka SETTINGS
   kafka_topic_list = 'topic1,topic2',
   kafka_group_name = 'group1',
   kafka_format = 'JSONEachRow',
-  kafka_row_delimiter = '\n'
+  kafka_row_delimiter = '\n',
   kafka_schema = '',
   kafka_num_consumers = 2
 ```