Typo fix in addons.md
Typo fix in addons.md

Two changes:
Kubernetes is in capital and lowercase letters.
addons is ->addons are
aledbf/kops,robinpercy/kops,gambol99/kops,robinpercy/kops,justinsb/kops,gambol99/kops,blakebarnett/kops,kubernetes/kops,blakebarnett/kops,aledbf/kops,gambol99/kops,tsupertramp/kops,blakebarnett/kops,tsupertramp/kops,aledbf/kops,justinsb/kops,gambol99/kops,tsupertramp/kops,aledbf/kops,tsupertramp/kops,kubernetes/kops,blakebarnett/kops,robinpercy/kops,kubernetes/kops,justinsb/kops,robinpercy/kops