docs: fix aggregate_functions link. (#1991)

Signed-off-by: t_max <1172915550@qq.com>

docs/en_US/README.md

@@ -78,7 +78,7 @@ Refer to the syntax and properties.
 - [Rule Syntax](./guide/rules/overview.md)
 - [Available Sources](./guide/sources/overview.md)
 - [Available Sinks](./guide/sinks/overview.md)
-- [Available Functions](./sqls/functions/overview.md
+- [Available Functions](./sqls/functions/overview.md)
 - [SQL Reference](./sqls/overview.md)
 
 [View Reference](./sqls/overview.md)
@@ -109,7 +109,7 @@ If you get stuck, check out our community support resources.
 - Ask in the [forum](https://askemq.com/c/ekuiper).
 - Join our [Slack](https://slack.lfedge.org/), and then join [ekuiper](https://lfedge.slack.com/archives/C024F4P7KCK) or [ekuiper-user](https://lfedge.slack.com/archives/C024F4SMEMR) channel.
 - Mail to eKuiper help [mail list](mailto:ekuiper+help@lists.lfedge.org).
-- Join WeChat group, scan the below QR code and mark "eKuiper". 
+- Join WeChat group, scan the below QR code and mark "eKuiper".
   
   <img src="./wechat.png" alt="drawing" width="200"/>
 
@@ -118,4 +118,4 @@ If you get stuck, check out our community support resources.
 Anyone can contribute for anything, not just code.
 
 - [Edit Doc in GitHub](https://github.com/lf-edge/ekuiper/tree/master/docs)
-- [How to contribute](./CONTRIBUTING.md)
+- [How to contribute](./CONTRIBUTING.md)

docs/en_US/sqls/functions/overview.md

@@ -2,7 +2,7 @@
 
 eKuiper has many built-in functions for performing calculations on data.
 
-- [Aggregate Functions](./aggregate_functions)
+- [Aggregate Functions](./aggregate_functions.md)
 - [Math Functions](./mathematical_functions.md)
 - [String Functions](./string_functions.md)
 - [Array Functions](./array_functions.md)
@@ -13,7 +13,7 @@ eKuiper has many built-in functions for performing calculations on data.
 - [Other Functions](./other_functions.md)
 
 
-- [Analytic Functions](./analytic_functions)
+- [Analytic Functions](./analytic_functions.md)
 - [Multi-Row Functions](./multi_row_functions.md
 - [Multi-Column Functions](./multi_column_functions.md)
 

docs/zh_CN/sqls/functions/overview.md

@@ -2,7 +2,7 @@
 
 eKuiper 具有许多内置函数，可以对数据执行计算。
 
-- [聚合函数](./aggregate_functions)
+- [聚合函数](./aggregate_functions.md)
 - [数学函数](./mathematical_functions.md)
 - [字符串函数](./string_functions.md)
 - [数组函数](./array_functions.md)
@@ -13,7 +13,7 @@ eKuiper 具有许多内置函数，可以对数据执行计算。
 - [其他函数](./other_functions.md)
 
 
-- [分析函数](./analytic_functions)
+- [分析函数](./analytic_functions.md)
 - [多行函数](./multi_row_functions.md)
 - [多列函数](./multi_column_functions.md)