go12: automatically install godoc/go vet
go12: automatically install godoc/go vet

Sync with changes pushed to Homebrew/Homebrew recently on automatically
installing the widely requested godoc & go vet.

Closes #697.

Signed-off-by: Dominyk Tiller <53e438f55903875d07efdd98a8aaf887e7208dd3@gmail.com>

coeligena/homebrew-verscustomized,jimhe/homebrew-versions,Ashton-W/homebrew-versions,DomT4/homebrew-versions,heuermh/homebrew-versions,UniqMartin/homebrew-versions