Fix doc for pool op. (#1689)

doc/fluid/api_guides/low_level/layers/pooling.rst

@@ -20,7 +20,7 @@ PaddlePaddle中有针对定长图像特征的二维(pool2d)、三维卷积(pool3
 
 -  ``num_channels``\ : 用来确定输入的\ ``channel``\ 数量，如果未设置参数或设置为\ ``None``\ ，其实际值将自动设置为输入的\ ``channel``\ 数量。
 
--  ``pooling_type``\ : 接收\ ``avg``\ 和\ ``max``\ 2种类型之一作为pooling的方式，默认值为\ ``max``\ 。其中\ ``max``\ 意为最大池化，即计算池化\ ``filter``\ 区域内的数据的最大值作为输出；而\ ``avg``\ 意为平均池化，即计算池化\ ``filter``\ 区域内的数据的平均值作为输出。
+-  ``pool_type``\ : 接收\ ``avg``\ 和\ ``max``\ 2种类型之一作为pooling的方式，默认值为\ ``max``\ 。其中\ ``max``\ 意为最大池化，即计算池化\ ``filter``\ 区域内的数据的最大值作为输出；而\ ``avg``\ 意为平均池化，即计算池化\ ``filter``\ 区域内的数据的平均值作为输出。
 
 -  ``pool_stride``\ : 意为池化的\ ``filter``\ 在输入特征图上移动的步长。
 

doc/fluid/api_guides/low_level/layers/pooling_en.rst

@@ -20,7 +20,7 @@ PaddlePaddle has two-dimensional (pool2d), three-dimensional convolution (pool3d
 
 - ``num_channels`` : It is used to determine the number of ``channel`` of input. If it is not set or is set to ``None``, its actual value will be automatically set to the ``channel`` quantity of input.
 
-- ``pooling_type`` : It receives one of ``agg`` and ``max`` as the pooling method. The default value is  ``max`` . ``max`` means maximum pooling, i.e. calculating the maximum value of the data in the pooled ``filter`` area as output; and ``avg`` means averaging pooling, i.e. calculating the average of the data in the pooled  ``filter`` area as output.
+- ``pool_type`` : It receives one of ``agg`` and ``max`` as the pooling method. The default value is  ``max`` . ``max`` means maximum pooling, i.e. calculating the maximum value of the data in the pooled ``filter`` area as output; and ``avg`` means averaging pooling, i.e. calculating the average of the data in the pooled  ``filter`` area as output.
 
 - ``pool_stride`` : It is the stride size in which the pooling ``filter`` moves on the input feature map.