fixed a small bug when using matplotlib

src/main/resources/templates/gluon/saveAttentionImageTrain.ftl

                     if save_attention_image == "True":
+                        import matplotlib
+                        matplotlib.use('Agg')
                         import matplotlib.pyplot as plt
                         logging.getLogger('matplotlib').setLevel(logging.ERROR)
 

src/test/resources/target_code/CNNSupervisedTrainer_Alexnet.py

@@ -341,6 +341,8 @@ class CNNSupervisedTrainer_Alexnet:
 
 
                     if save_attention_image == "True":
+                        import matplotlib
+                        matplotlib.use('Agg')
                         import matplotlib.pyplot as plt
                         logging.getLogger('matplotlib').setLevel(logging.ERROR)
 

src/test/resources/target_code/CNNSupervisedTrainer_CifarClassifierNetwork.py

@@ -341,6 +341,8 @@ class CNNSupervisedTrainer_CifarClassifierNetwork:
 
 
                     if save_attention_image == "True":
+                        import matplotlib
+                        matplotlib.use('Agg')
                         import matplotlib.pyplot as plt
                         logging.getLogger('matplotlib').setLevel(logging.ERROR)
 

src/test/resources/target_code/CNNSupervisedTrainer_VGG16.py

@@ -341,6 +341,8 @@ class CNNSupervisedTrainer_VGG16:
 
 
                     if save_attention_image == "True":
+                        import matplotlib
+                        matplotlib.use('Agg')
                         import matplotlib.pyplot as plt
                         logging.getLogger('matplotlib').setLevel(logging.ERROR)