Update tf.case.md

tensorflow2fluid/doc/tf.case.md

@@ -12,7 +12,7 @@ tf.case(
 )
 ```
 
-### [paddle.fluid.layers.While](http://paddlepaddle.org/documentation/docs/zh/1.3/api_cn/layers_cn.html#while)
+### [paddle.fluid.layers.While](http://paddlepaddle.org/documentation/docs/zh/1.4/api_cn/layers_cn.html#while)
 ```python
 class paddle.fluid.layers.Switch(
     name=None