Drop python 3.5 support

[mayeut]

Python 3.5 reached its end-of-life, time to drop support.

Repairing python 3.5 wheels is still supported.

[codecov]

Codecov Report

Merging #261 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #261   +/-   ##
=======================================
  Coverage   90.06%   90.06%           
=======================================
  Files          20       20           
  Lines        1057     1057           
  Branches      226      226           
=======================================
  Hits          952      952           
  Misses         62       62           
  Partials       43       43           

Impacted Files	Coverage Δ
auditwheel/policy/__init__.py	93.33% <100.00%> (ø)
auditwheel/repair.py	85.59% <100.00%> (ø)

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