build: convert to go:build directives

[thinkerou]

currently, CI fails on go master branch.

as mentioned in golang/go#41184 and golang/go#44505, Go will probably migrate to a more robust build constraints directive, as explained design doc:

https://golang.org/s/go-build-design

so, we should prepare for that:

for Go-1.17: add all //go:build directives
for Go-1.18: remove all // +build directives

[codecov]

Codecov Report

Merging #2664 (5428711) into master (1bdf86b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2664   +/-   ##
=======================================
  Coverage   98.64%   98.64%           
=======================================
  Files          41       41           
  Lines        1989     1989           
=======================================
  Hits         1962     1962           
  Misses         15       15           
  Partials       12       12           

Impacted Files	Coverage Δ
binding/binding.go	100.00% <ø> (ø)
binding/binding_nomsgpack.go	100.00% <ø> (ø)
binding/msgpack.go	100.00% <ø> (ø)
render/msgpack.go	100.00% <ø> (ø)

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[thinkerou]

@appleboy maybe we should review and merge the pr at first, thanks!