update interface

Signed-off-by: N冯泽悟 <fengzewu@huawei.com>

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

@@ -949,7 +949,7 @@ createImageSource(uri: string): ImageSource
 ```js
 //Stage模型
 const context = getContext(this);
-const path = context.getCacheDir() + "/test.jpg";
+const path = context.cacheDir() + "/test.jpg";
 const imageSourceApi = image.createImageSource(path);
 ```