feat: update go version to 1.16

[Windfarer]

use go 1.16

[codecov-commenter]

Codecov Report

Merging #1536 (05e53fe) into main (d0c65fb) will decrease coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1536      +/-   ##
==========================================
- Coverage   68.73%   68.60%   -0.13%     
==========================================
  Files          67       67              
  Lines        3090     3090              
==========================================
- Hits         2124     2120       -4     
- Misses        788      790       +2     
- Partials      178      180       +2     

Impacted Files	Coverage Δ
config/file/watcher.go	59.37% <0.00%> (-6.25%)	⬇️
config/file/file.go	61.90% <0.00%> (-4.77%)	⬇️

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[kagaya85]

LGTM