Upgrade jupyterhub to 0.7.2

[stefanoborini]

Fixes #354

[codecov-io]

Codecov Report

Merging #355 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #355      +/-   ##
==========================================
+ Coverage   95.17%   95.21%   +0.04%     
==========================================
  Files          92       92              
  Lines        3873     3891      +18     
  Branches      250      254       +4     
==========================================
+ Hits         3686     3705      +19     
  Misses        127      127              
+ Partials       60       59       -1

Impacted Files	Coverage Δ
remoteappmanager/utils.py	86.53% <100%> (+2.44%)	✅
remoteappmanager/command_line_config.py	100% <100%> (+4%)	✅
remoteappmanager/jupyterhub/tests/test_spawners.py	92.39% <100%> (ø)	✅
remoteappmanager/tests/utils.py	92.53% <100%> (+0.11%)	✅
remoteappmanager/tests/test_command_line_config.py	100% <100%> (ø)	✅
remoteappmanager/tests/test_utils.py	100% <100%> (ø)	✅

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