try to avoid possible memory leaks

docs/freqai-configuration.md

@@ -252,9 +252,9 @@ The `CNNPredictionModel` is a non-linear regression based on `Tensorflow` which
         "batch_size": 64,
         "epochs": 10,
         "verbose": "auto",
-        "shuffle": false
+        "shuffle": false,
         "workers": 1,
-        "use_multiprocessing": False
+        "use_multiprocessing": false
     }
 ```
 

freqtrade/freqai/prediction_models/CNNPredictionModel.py

@@ -133,6 +133,7 @@ class CNNPredictionModel(BaseTensorFlowModel):
         else:
             data = dk.data_dictionary["prediction_features"]
             data = tf.expand_dims(data, axis=0)
+            data = tf.convert_to_tensor(data)
             predictions = self.model(data, training=False)
 
         predictions = predictions[:, 0, 0]