Fix : optimizer_func is not callable

01.fit_a_line/README.cn.md

@@ -157,7 +157,7 @@ place = fluid.CUDAPlace(0) if use_cuda else fluid.CPUPlace()
 trainer = fluid.Trainer(
     train_func=train_program,
     place=place,
-    optimizer_func=fluid.optimizer.SGD(learning_rate=0.001))
+    optimizer_func=lambda : fluid.optimizer.SGD(learning_rate=0.001))
 ```
 
 ### 开始提供数据

01.fit_a_line/README.md

@@ -165,7 +165,7 @@ The trainer will take the `train_program` as input.
 trainer = fluid.Trainer(
     train_func=train_program,
     place=place,
-    optimizer_func=fluid.optimizer.SGD(learning_rate=0.001))
+    optimizer_func=lambda : fluid.optimizer.SGD(learning_rate=0.001))
 ```
 
 ### Feeding Data