sqlserverwriter的doc中column的描述有错误。

[sqlserverwriter](https://github.com/alibaba/DataX/blob/master/sqlserverwriter/doc/sqlserverwriter.md)

> 描述：目的表需要写入数据的字段,字段之间用英文逗号分隔。例如: "column": ["id","name","age"]。如果>
> 要依次写入全部列，使用表示, 例如: "column": [""]

会报错：
> Caused by: com.microsoft.sqlserver.jdbc.SQLServerException: 关键字 'from' 附近有语法错误

原因： "column": [""] 应该为： "column": ['*']

Open doc/sqlserverwriter.md and review the documented column examples against the reported SQL Server error. Correct the example for selecting all columns, then verify that the description consistently uses the valid syntax and no longer presents the failing form.

Written by the indexing model from the issue text.