update statfs apis

Signed-off-by: Nzhangxingxia <zhangxingxia1@huawei.com>

zh-cn/application-dev/reference/apis/js-apis-statfs.md

@@ -64,7 +64,7 @@ getFreeBytes(path:string, callback:AsyncCallback<number>): void
 - 示例：
 
   ```
-  statfs.getFreeBytes(path,function(err,number){
+  statfs.getFreeBytes(path, function(err, number){
       //do something
   });
   ```
@@ -109,7 +109,7 @@ getTotalBytes(path:string, callback:AsyncCallback<number>): void
 - 示例：
 
   ```
-  statfs.getTotalBytes(path,function(err, number){
+  statfs.getTotalBytes(path, function(err, number){
       //do something
   });
   ```