make default retry not on middlewares errors

[lrita]

This patch make default retry not on middlewares errors, which will make the retry action more sense and return error faster.

[codecov]

Codecov Report

Merging #333 into master will increase coverage by 0.04%.
The diff coverage is 90.90%.

@@            Coverage Diff             @@
##           master     #333      +/-   ##
==========================================
+ Coverage   95.64%   95.69%   +0.04%     
==========================================
  Files           9        9              
  Lines        1195     1207      +12     
==========================================
+ Hits         1143     1155      +12     
  Misses         30       30              
  Partials       22       22              

Impacted Files	Coverage Δ
client.go	96.87% <60.00%> (ø)
request.go	100.00% <100.00%> (ø)
retry.go	97.36% <100.00%> (+0.03%)	⬆️
util.go	90.85% <100.00%> (+0.59%)	⬆️

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[jeevatkm]

@lrita Thanks for the PR and enhancing retry error handling.