update comments

Author: RuiboZhang1

src/main/java/cn/jpush/api/image/ImageClient.java

@@ -142,7 +142,8 @@ public ImageUploadResult modifyImage(String mediaId, ImageUrlPayload imageUrlPay
      * @throws APIConnectionException connection exception
      * @throws APIRequestException request exception
      */
-    public ImageUploadResult modifyImage(String mediaId, ImageFilePayload imageFilePayload) {
+    public ImageUploadResult modifyImage(String mediaId, ImageFilePayload imageFilePayload)
+            throws APIConnectionException, APIRequestException {
         Preconditions.checkArgument(StringUtils.isNotEmpty(mediaId), "mediaId should not be empty");
         checkImageFilePayload(imageFilePayload);
         NativeHttpClient client = (NativeHttpClient) _httpClient;