Update *.ipynb metadata from python2 to python3

[JohnTigue]

This is a Python 2 vs 3 thing. Notebooks call for python2 so Colab gets confused, or warns that Python 2 is deprecated. And it's 2020, RIP python2.

AllenSDK docs:

The Allen SDK was developed and tested with Python 2.7.13 and Python 3.6.4,

A example of python2 is in BrainObservatory.ipynb:

 "metadata": {
  "kernelspec": {
     "display_name": "Python 2",
     "language": "python",
     "name": "python2"
    },
  "language_info": {
     "codemirror_mode": {
      "name": "ipython",
      "version": 2
     },
   "file_extension": ".py",
     "mimetype": "text/x-python",
     "name": "python",
     "nbconvert_exporter": "python",
     "pygments_lexer": "ipython2",
     "version": "2.7.15"
    }

[JohnTigue]

• [ ] DynamicBrain/Neuropixels_walkthrough.ipynb
• [ ] DynamicBrain/EM_Connectomics_Question_3.ipynb
• [ ] DynamicBrain/Neuropixels_exercises.ipynb
• [ ] DynamicBrain/EM_Connectomics_Question_1.ipynb
• [ ] DynamicBrain/Other/Connectivity.ipynb
• [ ] DynamicBrain/Other/BrainObservatory.ipynb
• [ ] DynamicBrain/VisualBehavior_Exercises.ipynb
• [ ] DynamicBrain/solutions/EM_Connectomics_Question_1_solutions.ipynb
• [ ] DynamicBrain/solutions/Other/BrainObservatory_solutions.ipynb
• [ ] DynamicBrain/solutions/Other/CellTypes_solutions.ipynb
• [ ] DynamicBrain/solutions/Other/Connectivity_solutions.ipynb
• [ ] DynamicBrain/solutions/VisualBehavior_Exercises_Solutions.ipynb
• [ ] DynamicBrain/solutions/Neuropixels_exercises_solutions.ipynb
• [ ] DynamicBrain/solutions/EM_Connectomics_Question_2_solutions.ipynb
• [ ] DynamicBrain/solutions/VisualBehavior_Tutorial_Solutions.ipynb
• [ ] DynamicBrain/solutions/EM_Connectomics_Question_3_solutions.ipynb
• [ ] DynamicBrain/EM_Connectomics_Question_2.ipynb
• [ ] DynamicBrain/VisualBehavior_Tutorial.ipynb
• [ ] DynamicBrain/Tutorials/T01_Regression.ipynb
• [ ] DynamicBrain/Tutorials/T03_Classification_tutorial.ipynb
• [ ] DynamicBrain/Tutorials/solutions/01_decoding_sklearn_solutions.ipynb
• [ ] DynamicBrain/Tutorials/T04_Pipelines.ipynb
• [ ] DynamicBrain/Tutorials/01_decoding_sklearn.ipynb
• [ ] DynamicBrain/Tutorials/T02_Principal_component_analysis.ipynb
• [ ] DynamicBrain/EM_Connectome_Intro.ipynb
• [ ] Credits.ipynb
• [ ] PythonBootcamp/06_Introduction_To_Matplotlib.ipynb
• [ ] PythonBootcamp/02_Basic_Python_II_Control_Flow_and_Functions.ipynb
• [ ] PythonBootcamp/04_Introduction_To_Numpy.ipynb
• [ ] PythonBootcamp/00_Introduction.ipynb
• [ ] PythonBootcamp/07_Introduction_To_Pandas.ipynb
• [ ] PythonBootcamp/08_Development_Tools.ipynb
• [ ] PythonBootcamp/05_Custom_Modules_and_Version_Control.ipynb
• [ ] PythonBootcamp/01_Basic_Python_I_Object_and_Data_Structures.ipynb
• [ ] PythonBootcamp/Other/09_bike_crossing.ipynb
• [ ] PythonBootcamp/Other/10_glm_exercise.ipynb
• [ ] PythonBootcamp/Other/11_Image_data.ipynb
• [ ] PythonBootcamp/solutions/05_Custom_Modules_and_Version_Control_solutions.ipynb
• [ ] PythonBootcamp/solutions/07_Introduction_To_Pandas_solutions.ipynb
• [ ] PythonBootcamp/solutions/01_Basic_Python_I_Object_and_Data_Structures_solutions.ipynb
• [ ] PythonBootcamp/solutions/06_Introduction_To_Matplotlib_solutions.ipynb
• [ ] PythonBootcamp/solutions/Other/11_Image_data_solutions.ipynb
• [ ] PythonBootcamp/solutions/Other/09_bike_crossing_solutions.ipynb
• [ ] PythonBootcamp/solutions/04_Introduction_To_Numpy_solutions.ipynb
• [ ] PythonBootcamp/solutions/03_Intro_To_Scientific_Computing_solutions.ipynb
• [ ] PythonBootcamp/solutions/02_Basic_Python_II_Control_Flow_and_Functions_solutions.ipynb
• [ ] PythonBootcamp/03_Intro_To_Scientific_Computing.ipynb

Was calling for python2

• [ ] DynamicBrain/Other/CellTypes.ipynb