klaytn package management is migrated from Dep to Go Modules about klaytn

[miloveme]

In klaytn project, Makefile should be modified to use Go Module
Makefile :
...
build/env.sh go run build/ci.go install ./cmd/kcn
...
all of 'build/env.sh' is removed because Go Module doesn't need go environment

[miloveme]

If you want to keep your vendor folder:
do not 7 step mentioned and do following step instead of 7 step
7. Run go mod vendor to copy your dependencies into the vendor folder.
8. Run go build -mod=vendor to ensure go build uses your vendor folder.