Fix application exit

[afshin]

No description provided.

[codecov-io]

Codecov Report

Merging #384 (7a04ce2) into master (3135bd6) will decrease coverage by 0.03%.
The diff coverage is 20.00%.

@@            Coverage Diff             @@
##           master     #384      +/-   ##
==========================================
- Coverage   69.28%   69.25%   -0.04%     
==========================================
  Files          56       56              
  Lines        6128     6131       +3     
  Branches      798      798              
==========================================
  Hits         4246     4246              
- Misses       1616     1619       +3     
  Partials      266      266              

Impacted Files	Coverage Δ
jupyter_server/extension/application.py	61.34% <20.00%> (-0.97%)	⬇️

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[Zsailer]

👍 The test failures appear unrelated to this PR. I'm not sure what's happening on PyPy... Merging as-is.