The Minishift installation has the oc tool by default already and it is not required be download and/or installed. In order to use it is required just do the following setup.
Run the command : $minishift oc-env
PS.: The Minishift needs to be started.
Then, the following output will appear.
# Run this command to configure your shell:
# eval $(minishift oc-env)
Now, to be able to use the oc tool in the shell terminal just run the following command as explained in the above output.
eval $(minishift oc-env)
For further information see <https://docs.openshift.org/latest/minishift/command-ref/minishift_oc-env.html>.