Save time Last-Modified to output file

[gonejack]

Hi,

This PR saves header time "last-modified" to output file.

[codecov[bot]]

Codecov Report

Merging #493 (c830781) into master (313f419) will decrease coverage by 0.45%. The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #493      +/-   ##
==========================================
- Coverage   96.69%   96.24%   -0.45%     
==========================================
  Files          10       10              
  Lines        1330     1333       +3     
==========================================
- Hits         1286     1283       -3     
- Misses         26       31       +5     
- Partials       18       19       +1     

Impacted Files	Coverage Δ
middleware.go	92.22% <33.33%> (-0.64%)	:arrow_down:
request.go	96.35% <0.00%> (-1.46%)	:arrow_down:

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[jeevatkm]

@gonejack I'm sorry for the delayed attention on the PR. Can you please add test coverage for this PR? See here - https://github.com/go-resty/resty/pull/493/checks?check_run_id=11777873655

Once ready we can merge this PR!

[gonejack]

@jeevatkm Yes, but need some time, since this PR is made by 2021.

[jeevatkm]

@gonejack Thanks for your contribution. I thought about this PR, I think we should make this as opt-in option to use last modified date from the response header. I will take up this later on. For now I'm closing this one.