fix example code error (#2226)

doc/fluid/api_cn/layers_cn/double_buffer_cn.rst

@@ -25,12 +25,12 @@ double_buffer
 ..  code-block:: python
 
     import paddle.fluid as fluid
-  reader = fluid.layers.open_files(filenames=['mnist.recordio'],
-           shapes=[[-1, 784], [-1, 1]],
-           lod_levels=[0, 0],
-           dtypes=['float32', 'int64'])
+    reader = fluid.layers.py_reader(capacity=64,
+                                    shapes=[(-1, 1, 28, 28), (-1, 1)],
+                                    dtypes=['float32', 'int64'],
+                                    use_double_buffer=False)
     reader = fluid.layers.double_buffer(reader)
-  img, label = fluid.layers.read_file(reader)
+    image, label = fluid.layers.read_file(reader)
 
 
 

doc/fluid/api_cn/layers_cn/py_reader_cn.rst

@@ -113,7 +113,6 @@ py_reader
                                                 dtypes=['float32', 'int64'],
                                                 name='test_reader')
             test_reader.decorate_paddle_reader(paddle.batch(mnist.test(), 512))
-    
             test_loss = network(test_reader)
 
     fluid.Executor(fluid.CUDAPlace(0)).run(train_startup_prog)