fix dotenv package version

Keras_Tensorflow/tutorial_env.yml

@@ -8,7 +8,7 @@ dependencies:
 - pip:
     # Required packages for AzureML execution, history, and data preparation.
   - papermill==0.14.1
-  - python-dotenv==0.9.0
+  - python-dotenv==0.10.1
   - Pillow==5.2.0
   - wget==3.2
   - matplotlib==2.2.2