[bug] Fix debian_nextcodename on wheezy hosts

I noticed this behaviour because $::debian_nextcodename was
"squeeze" on a wheezy host.
For debugging, i inserted a "puts codenames" in
lib/facter/debian_nextcodename.rb, and it turned out that it
was sorted differently on wheezy and jessie hosts:

On wheezy:

    buster
    stretch
    jessie
    wheezy
    squeeze
    lenny

On jessie:

    lenny
    squeeze
    wheezy
    jessie
    stretch
    buster

So i decided to rewrite this so this doesn't happen again.

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/facter/util/ubuntu.rb b/lib/facter/util/ubuntu.rb
index 1b2411a..52c15e8 100644
--- a/lib/facter/util/ubuntu.rb
+++ b/lib/facter/util/ubuntu.rb
@@ -14,6 +14,7 @@ module Facter
         "utopic",
         "vivid",
         "wily",
+        "xenial"
       ]
     end
   end