Github fix permission denied error

when using go mod to get private dependencies.

Example error

go: github.com/account/project-utils@v0.0.0-20201015040921-5f23d1a17a73: invalid version: git fetch -f origin refs/heads/*:refs/heads/* refs/tags/*:refs/tags/* in /home/cuongld/go/pkg/mod/cache/vcs/asshfsfsd: exit status 128:
        git@github.com: Permission denied (publickey).
        fatal: Could not read from remote repository.
        
        Please make sure you have the correct access rights
        and the repository exists.