not use protobuf on context but use it on render

[thinkerou]

ref #1479
please @salamer @appleboy help review, thanks!

[codecov]

Codecov Report

Merging #1496 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1496   +/-   ##
=======================================
  Coverage   99.16%   99.16%           
=======================================
  Files          37       37           
  Lines        1905     1905           
=======================================
  Hits         1889     1889           
  Misses         13       13           
  Partials        3        3

Impacted Files	Coverage Δ
render/json.go	100% <ø> (ø)	⬆️
render/render.go	100% <ø> (ø)	⬆️
context.go	99.49% <100%> (ø)	⬆️
render/protobuf.go	100% <100%> (ø)	⬆️

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