doc: format code in doc file

docs/mathutil_zh-CN.md

@@ -789,7 +789,6 @@ func main() {
 }
 ```
 
-
 ### <span id="Cos">Cos</span>
 
 <p>计算弧度的余弦值</p>
@@ -832,7 +831,6 @@ func main() {
 }
 ```
 
-
 ### <span id="Sin">Sin</span>
 
 <p>计算弧度的正弦值</p>

docs/structs/field.md

@@ -21,6 +21,7 @@ import (
 <div STYLE="page-break-after: always;"></div>
 
 ## Index:
+
 -   [Tag](#Tag)
 -   [Name](#Name)
 -   [Value](#Value)

docs/structs/struct.md

@@ -21,6 +21,7 @@ import (
 <div STYLE="page-break-after: always;"></div>
 
 ## Index:
+
 -   [New](#New)
 -   [ToMap](#ToMap)
 -   [Fields](#Fields)

docs/structs/struct_zh-CN.md

@@ -21,6 +21,7 @@ import (
 <div STYLE="page-break-after: always;"></div>
 
 ## 目录:
+
 -   [New](#New)
 -   [ToMap](#ToMap)
 -   [Fields](#Fields)

docs/strutil.md

@@ -1322,7 +1322,6 @@ func main() {
 }
 ```
 
-
 ### <span id="ContainsAll">ContainsAll</span>
 
 <p>Return true if target string contains all the substrings.</p>
@@ -1392,7 +1391,6 @@ func main() {
 }
 ```
 
-
 ### <span id="RemoveWhiteSpace">RemoveWhiteSpace</span>
 
 <p>Remove whitespace characters from a string. when set repalceAll is true removes all whitespace, false only replaces consecutive whitespace characters with one space.</p>