[BUGFIX] correct variable used in install_golang.yml

Should be `update_etc_environment_path_script_server_sha256_sum` instead
of `update_etc_environment_path_server_sha256_sum`

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>
install_golang.yml - use `shasum` program for Mac OS X

This is for obtaining the sha256sum of a file on the host machine.
Apparently Mac OS X does not have a sha256sum program.

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>