add 1.6 requirement (#830)

03.image_classification/README.cn.md

@@ -14,6 +14,7 @@
 3.文档和脚本中代码的一致性问题：
 请注意：为使本文更加易读易用，我们拆分、调整了train.py的代码并放入本文。本文中代码与train.py的运行结果一致，可直接运行[train.py](https://github.com/PaddlePaddle/book/blob/develop/03.image_classification/train.py)进行验证。
 
+4. PaddlePaddle版本：PaddlePaddle 1.6及以上版本或适当的develop版本。
 
 ## 背景介绍
 

03.image_classification/README.md

@@ -15,6 +15,10 @@ With Deep learning, image classification can be framed as a supervised or unsupe
 
 In this chapter, we introduce deep-learning-based image classification methods and explain how to train a CNN model using PaddlePaddle.
 
+## Requirement
+
+1. PaddlePaddle version 1.6 or higher, or suitable develop version.
+
 ## Result Demo
 
 Image Classification can be divided into general image classification and fine-grained image classification.

03.image_classification/index.cn.html

@@ -56,6 +56,7 @@
 3.文档和脚本中代码的一致性问题：
 请注意：为使本文更加易读易用，我们拆分、调整了train.py的代码并放入本文。本文中代码与train.py的运行结果一致，可直接运行[train.py](https://github.com/PaddlePaddle/book/blob/develop/03.image_classification/train.py)进行验证。
 
+4. PaddlePaddle版本：PaddlePaddle 1.6及以上版本或适当的develop版本。
 
 ## 背景介绍
 

03.image_classification/index.html

@@ -57,6 +57,10 @@ With Deep learning, image classification can be framed as a supervised or unsupe
 
 In this chapter, we introduce deep-learning-based image classification methods and explain how to train a CNN model using PaddlePaddle.
 
+## Requirement
+
+1. PaddlePaddle version 1.6 or higher, or suitable develop version.
+
 ## Result Demo
 
 Image Classification can be divided into general image classification and fine-grained image classification.