fix links in sandbox.md

packages/app/resource/locales/en_US/sandbox.md

@@ -256,7 +256,7 @@ Both the page description and link address can be displayed on the page.
 Example of Bootstrap4 is [[here>./Bootstrap4]]
 ```
 
-[[../Bootstrap4]]  
+[[./Bootstrap4]]  
 Example of Bootstrap4 is[[here>./Bootstrap4]]
 
 # :pencil: Lists

packages/app/resource/locales/ja_JP/sandbox.md

@@ -255,7 +255,7 @@ ___
 Bootstrap4のExampleは[[こちら>./Bootstrap4]]
 ```
 
-[[../Bootstrap4]]  
+[[./Bootstrap4]]  
 Bootstrap4のExampleは[[こちら>./Bootstrap4]]
 
 # :pencil: Lists

packages/app/resource/locales/zh_CN/sandbox.md

@@ -256,7 +256,7 @@ Both the page description and link address can be displayed on the page.
 Example of Bootstrap4 is[[here>./Bootstrap4]]
 ```
 
-[[../Bootstrap4]]  
+[[./Bootstrap4]]  
 Example of Bootstrap4 is [[here>./Bootstrap4]]
 
 # :pencil: Lists