Change the way to save custom variables.

I changed custom-set-variables&&custom-save-all by
customize-save-variable. I guess that is the standard way and with the
custom-set-variables I received this error message:

"Error setting helm-dash-active-docsets: (invalid-function Ansible)"
Merge pull request #9 from areina/fix-helm-dash-activate-docset

Change the way to save custom variables.