Fix image aspect ratio (#1224)

* fix images

fluid/face_detection/README_cn.md

@@ -168,10 +168,11 @@ python widerface_eval.py --infer=True --confs_threshold=0.15
 <img src="images/0_Parade_marchingband_1_356.jpg" height=300 width=300 hspace='10'/>
 <img src="images/28_Sports_Fan_Sports_Fan_28_770.jpg" height=300 width=300 hspace='10'/>
 <img src="images/4_Dancing_Dancing_4_194.jpg" height=300 width=300 hspace='10'/>
-<img src="images/2_Demonstration_Demonstration_Or_Protest_2_58.jpg" height=300 width=300 hspace='10'/>  <br />
+<img src="images/12_Group_Group_12_Group_Group_12_935.jpg" height=300 width=300 hspace='10'/>  <br />
 Pyramidbox 预测可视化
 </p>
 
+
 ### 模型发布
 
 
@@ -187,5 +188,3 @@ Pyramidbox 预测可视化
     <img src="images/wider_pr_cruve_int_hard_val.jpg" width="280" /></br>
 WIDER FACE Easy/Medium/Hard set
 </p>
-
-> 目前，基于PaddlePaddle的实现过程中模型参数仍在调优，比上图更优的结果会在后续发布