Change :user to :owner

For the two projects I've looked at that use this, their main.json files use 'group' and 'owner', but this recipe was using 'group' and 'user'.  I changed the recipe to match the main.json files ('owner' instead of 'user'), but this may break other projects that use this if they were providing different values for 'user' and 'owner'.  You may want to check for that.