fix format error

tiflash/use-tiflash.md

@@ -242,7 +242,7 @@ TiFlash 支持部分算子的下推，支持的算子如下：
 JSON 函数: json_length
 转换函数: cast(int as double), cast(int as decimal), cast(int as string), cast(int as time), cast(double as int), cast(double as decimal), cast(double as string), cast(double as time), cast(string as int), cast(string as double), cast(string as decimal), cast(string as time), cast(decimal as int), cast(decimal as string), cast(decimal as time), cast(time as int), cast(time as decimal), cast(time as string)
 聚合函数: min, max, sum, count, avg, approx_count_distinct
-`
+```
 
 其中，`cast` 和 `date_add` 的下推默认不开启，若需要手动开启，请参考[优化规则及表达式下推的黑名单](/blocklist-control-plan.md)