refine README (#402)

README.md

@@ -4,7 +4,7 @@
 
 PaddleDetection的目的是为工业界和学术界提供丰富、易用的目标检测模型。不仅性能优越、易于部署，而且能够灵活的满足算法研究的需求。
 
-**目前检测库下模型均要求使用PaddlePaddle 1.6及以上版本或适当的develop版本。**
+**目前检测库下模型均要求使用PaddlePaddle 1.7及以上版本或适当的develop版本。**
 
 <div align="center">
   <img src="docs/images/000000570688.jpg" />

README_en.md

@@ -7,7 +7,7 @@ detection models in both industry and research settings. We design
 PaddleDetection to be not only performant, production-ready but also highly
 flexible, catering to research needs.
 
-**Now all models in PaddleDetection require PaddlePaddle version 1.6 or higher, or suitable develop version.**
+**Now all models in PaddleDetection require PaddlePaddle version 1.7 or higher, or suitable develop version.**
 
 <div align="center">
   <img src="docs/images/000000570688.jpg" />