Fix double scheme output if set in site domain

[yakky]

Fix #62

[codecov]

Codecov Report

Merging #70 into master will increase coverage by 0.76%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #70      +/-   ##
==========================================
+ Coverage   64.92%   65.69%   +0.76%     
==========================================
  Files           7        7              
  Lines         134      137       +3     
  Branches       14       15       +1     
==========================================
+ Hits           87       90       +3     
  Misses         41       41              
  Partials        6        6

Impacted Files	Coverage Δ
robots/views.py	73.84% <100%> (+1.26%)	✅

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[yakky]

@tyapkov would you tests if this PR fixes your issues with #62 ?

[tyapkov]

@yakky update solves the problem, but now sitemap record in robots.txt is always shown with protocol.

[yakky]

@tyapkov is this comment still true after #62 (comment)?

[yakky]

I anyway rebased it on top of the current master which also includes the fix to detect the correct request protocol