Override Netty version to fix CVE-2020-11612

[gphilipp]

Checklist

• tests
• updated CHANGELOG (the "unreleased" section)

[codecov]

Codecov Report

Merging #261 (0c9d0a2) into master (e7f41ab) will decrease coverage by 0.38%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #261      +/-   ##
==========================================
- Coverage   81.22%   80.84%   -0.39%     
==========================================
  Files          41       41              
  Lines        2594     2594              
  Branches      153      153              
==========================================
- Hits         2107     2097      -10     
- Misses        334      344      +10     
  Partials      153      153              

Impacted Files	Coverage Δ
src/jackdaw/serdes/edn2.clj	45.45% <0.00%> (-45.46%)	⬇️

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[cddr]

btw @gphilipp, I think the only thing requiring netty in jackdaw is the test machine which I have now factored out into it's own repo (I think you can't get at it via jackdaw without merging this anyway #266).