Fix mot modules (#1690)

modules/video/multiple_object_tracking/fairmot_dla34/README.md

@@ -53,7 +53,7 @@
     ```
   - 通过命令行方式实现多目标追踪模型的调用，更多请见 [PaddleHub命令行指令](../../../../docs/docs_ch/tutorial/cmd_usage.rst)
 
-- ### 2、代码示例
+- ### 2、预测代码示例
 
   - ```python
     import paddlehub as hub

modules/video/multiple_object_tracking/fairmot_dla34/tracker.py

@@ -41,7 +41,8 @@ class StreamTracker(object):
         self.optimizer = None
 
         # build model
-        self.model = create(cfg.architecture)
+        with paddle.no_grad():
+            self.model = create(cfg.architecture)
 
         self.status = {}
         self.start_epoch = 0

modules/video/multiple_object_tracking/jde_darknet53/README.md

@@ -55,7 +55,7 @@
     ```
   - 通过命令行方式实现多目标追踪模型的调用，更多请见 [PaddleHub命令行指令](../../../../docs/docs_ch/tutorial/cmd_usage.rst)
 
-- ### 2、代码示例
+- ### 2、预测代码示例
 
   - ```python
     import paddlehub as hub