MAINT: Update JupyterHub to v0.8.1

[flongford]

Closes #397
Closes #596

This PR bumps the pinned version of jupyterhub to release 0.8.1

Changelog for 0.8.x series of JupyterHub: https://jupyterhub.readthedocs.io/en/stable/changelog.html#id44

Commit comparison between 0.8.1 and current pinned commit on master: jupyterhub/jupyterhub@2d1a45f...0.8.1

Major changes include:

• Replacing jupyterhub.orm.Proxy with jupyterhub.proxy.Proxy where appropriate
• Replacing jupyterhub.orm.Hub with jupyterhub.objects.Hub where appropriate
• Updating handling of BaseApplication settings between CommandLineConfig and EnvironmentConfig
• Adding a jupyterhub versioning check to the BaseApplication class (may not be required)
• Authenticating with JupyterHub as an OAuth provider, rather than using (deprecated) session cookie

[codecov-commenter]

Codecov Report

Merging #552 (b6c7ebc) into master (5cc033c) will decrease coverage by 0.24%.
The diff coverage is 86.01%.

❗ Current head b6c7ebc differs from pull request most recent head da197ae. Consider uploading reports for the commit da197ae to get more accurate results

@@            Coverage Diff             @@
##           master     #552      +/-   ##
==========================================
- Coverage   95.03%   94.79%   -0.25%     
==========================================
  Files          93       93              
  Lines        4350     4418      +68     
  Branches      429      432       +3     
==========================================
+ Hits         4134     4188      +54     
- Misses        156      168      +12     
- Partials       60       62       +2     

Impacted Files	Coverage Δ
remoteappmanager/command_line_config.py	100.00% <ø> (ø)
...ager/jupyterhub/auth/simphony_remote_auth_mixin.py	38.09% <20.00%> (+3.09%)	⬆️
remoteappmanager/tests/mocking/dummy.py	91.76% <33.33%> (+0.09%)	⬆️
remoteappmanager/base_application.py	88.63% <67.56%> (-8.34%)	⬇️
remoteappmanager/jupyterhub/spawners.py	87.87% <87.50%> (-0.67%)	⬇️
remoteappmanager/services/hub.py	97.05% <88.88%> (-2.95%)	⬇️
remoteappmanager/environment_config.py	100.00% <100.00%> (ø)
...anager/handlers/admin/tests/test_admin_handlers.py	100.00% <100.00%> (ø)
remoteappmanager/handlers/base_handler.py	97.05% <100.00%> (+0.39%)	⬆️
remoteappmanager/handlers/handler_authenticator.py	100.00% <100.00%> (ø)
... and 16 more

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