fix U2Net_Portrait module readme (#1708)

modules/image/Image_gan/style_transfer/U2Net_Portrait/README.md

@@ -50,16 +50,16 @@
 
 ## 三、模型API预测
 
-- ### 1、代码示例
+- ### 1、预测代码示例
 
   - ```python
     import paddlehub as hub
     import cv2
 
     model = hub.Module(name="U2Net_Portrait")
-    result = model.Cartoon_GEN(images=[cv2.imread('/PATH/TO/IMAGE')])
+    result = model.Portrait_GEN(images=[cv2.imread('/PATH/TO/IMAGE')])
     # or
-    # result = model.Cartoon_GEN(paths=['/PATH/TO/IMAGE'])
+    # result = model.Portrait_GEN(paths=['/PATH/TO/IMAGE'])
     ```
 
 - ### 2、API