update Go to 1.16, drop support for 1.14

[marten-seemann]

No description provided.

[marten-seemann]

Currently blocked by CircleCI, who, once again, are not able to provide a Docker image using the newly released Go version.
Time to say goodbye soon?

[vtolstov]

I'm recommending github actions, it have realy nice speed of execution.

[codecov]

Codecov Report

Merging #3045 (62a906d) into master (dd9f8e4) will increase coverage by 0.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3045      +/-   ##
==========================================
+ Coverage   86.03%   86.20%   +0.17%     
==========================================
  Files         135      131       -4     
  Lines        9490     9356     -134     
==========================================
- Hits         8164     8065      -99     
+ Misses        965      935      -30     
+ Partials      361      356       -5     

Impacted Files	Coverage Δ
internal/qtls/structs_equal.go	100.00% <ø> (ø)
stream.go	87.18% <100.00%> (+1.47%)	⬆️

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