fix: Koa.js handling of node.js set error codes

[vijaykrishnavanshi]

Fixes issue: #1451

[codecov]

Codecov Report

Merging #1460 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1460   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files           4        4           
  Lines         484      485    +1     
  Branches      130      132    +2     
=======================================
+ Hits          481      482    +1     
  Partials        3        3           

Impacted Files	Coverage Δ
lib/context.js	100.00% <100.00%> (ø)
lib/response.js	99.37% <0.00%> (ø)

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