subsetting.ipynb: update output for new Jupyter env

New Jupyter env in Ouranosinc/PAVICS-e2e-workflow-tests#85.

This is still weird as we are already ignoring by default all html
changes in
https://github.com/Ouranosinc/PAVICS-e2e-workflow-tests/blob/3172f621afe991c69caa0fa10c7d40f2f09fdd02/conftest.py#L5

Error fixed:
```
  _______ pavics-sdi-master/docs/source/notebooks/subsetting.ipynb::Cell 4 _______
  Notebook cell execution failed
  Cell 4: Cell outputs differ

  Input:
  res = resp.get()
  print("URL: ", res.output)
  res = resp.get(asobj=True)
  res.output

  Traceback:
   mismatch 'text/plain'

   assert reference_output == test_output failed:

    '<xarray.Data...        2.6.0' == '<xarray.Data...        2.6.0'
    Skipping 1136 identical trailing characters in diff, use -v to show
      <xarray.Dataset>
    - Dimensions:             (time: 12, bnds: 2, lat: 38, lon: 37)
    + Dimensions:             (bnds: 2, lat: 38, lon: 37, time: 12)
      Coordin
```