add support for Go 1.17 (tip)

[marten-seemann]

@mvdan Ready for Go 1.17 beta1! All we have to do is rebase the qtls repository onto the beta1 Go commit. Assuming that there won't be any significant changes to crypto/tls, that should be trivial.

[codecov]

Codecov Report

Merging #3182 (808c9c4) into master (e08cda5) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3182      +/-   ##
==========================================
- Coverage   85.38%   85.37%   -0.01%     
==========================================
  Files         133      133              
  Lines        9819     9819              
==========================================
- Hits         8383     8382       -1     
- Misses       1061     1062       +1     
  Partials      375      375              

Impacted Files	Coverage Δ
internal/qtls/go116.go	46.67% <ø> (ø)
internal/utils/rand.go	62.50% <0.00%> (-12.50%)	⬇️

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[mvdan]

As soon as 1.17 is released you'll be able to remove 1.15, too.

[marten-seemann]

As soon as 1.17 is released you'll be able to remove 1.15, too.

That's the plan. And as soon as the beta is out, we can also test this in CI.