5.7.14 breaks installation of notebook extensions.

[GaspardBT]

Describe the bug
The version 5.7.14 for python2breaks installation of notebook extensions. Running jupyter contrib nbextension install --user fails with TypeError: '_sre.SRE_Match' object has no attribute '__getitem__'

To Reproduce
Steps to reproduce the behavior:

1. Create a venv:

pyenv shell 2.7.18
virtualenv -p `which python` env2
source env2/bin/activate

2. Install jupyter:

pip install jupyter
pip install jupyter-nbextensions-configurator==0.4.1
pip install jupyter_contrib_nbextensions==0.5.1

3. Run jupyter contrib nbextension install --user

Expected behavior
Running jupyter contrib nbextension install --user should succeed.

Additional context
Reinstalling 5.7.13 (pip install notebook==5.7.13) resolve the issue. My understanding is that this commit introduce an issue. The following code

import re
__version__ = '5.7.14'
# Build up version_info tuple for backwards compatibility
pattern = r'(?P<major>\d+).(?P<minor>\d+).(?P<patch>\d+)(?P<rest>.*)'
match = re.match(pattern, __version__)
parts = [int(match[part]) for part in ['major', 'minor', 'patch']]
if match['rest']:
    parts.append(match['rest'])
version_info = tuple(parts)

It returns TypeError: '_sre.SRE_Match' object has no attribute '__getitem__' like in the described bug. According to this this syntax was only added with python3.6.
Replacing the code by the following one works.

import re

__version__ = '5.7.14'
# Build up version_info tuple for backwards compatibility
pattern = r'(?P<major>\d+).(?P<minor>\d+).(?P<patch>\d+)(?P<rest>.*)'
match = re.match(pattern, __version__)
parts = [int(match.group(part)) for part in ['major', 'minor', 'patch']]
if match.group('rest'):
    parts.append(match.group('rest'))
version_info = tuple(parts)

[RRosio]

Hi @GaspardBT thank you for submitting this issue and sharing your findings, your suggested changes were applied in the latest release of Notebook 5!

[RRosio]

I'll close this issue as resolved with the merged PR #6522. Thank you!