switch min version of go to 1.15

[thinkerou]

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[codecov]

Codecov Report

Merging #3211 (b81c692) into master (12b55b4) will decrease coverage by 0.15%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3211      +/-   ##
==========================================
- Coverage   98.22%   98.06%   -0.16%     
==========================================
  Files          43       43              
  Lines        3148     3148              
==========================================
- Hits         3092     3087       -5     
- Misses         44       48       +4     
- Partials       12       13       +1     

Flag	Coverage Δ
go-1.14	?
go-1.15	98.06% <0.00%> (ø)
go-1.16	98.03% <0.00%> (ø)
go-1.17	97.96% <0.00%> (ø)
go-1.18	97.96% <0.00%> (ø)
macos-latest	98.06% <0.00%> (-0.16%)	⬇️
nomsgpack	98.03% <0.00%> (-0.17%)	⬇️
ubuntu-latest	98.06% <0.00%> (-0.16%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
debug.go	91.66% <0.00%> (-8.34%)	⬇️

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