packaging: add Cosmic and Disco, remove Trusty and Artful - Trusty was publicly supported until 2019-04-30 - Artful was publicly supported until 2018-07-19 - Cosmic was publicly supported until 2019-07-18 - Disco will be publicly supported until 2020-01 Cosmic is officially out-of-date, but since it still may be in use, and because we didn't add it when it first came out, I think it would be nice to support it until the next time somebody decides to update this list of Ubuntu releases. Differential Revision: https://phab.mercurial-scm.org/D6761

--- a/contrib/packaging/Makefile	Wed Aug 21 17:56:50 2019 +0200
+++ b/contrib/packaging/Makefile	Sun Aug 25 19:38:09 2019 +0700
@@ -6,10 +6,10 @@
   buster
 
 UBUNTU_CODENAMES := \
-  trusty \
   xenial \
-  artful \
   bionic \
+  cosmic \
+  disco
 
 FEDORA_RELEASES := \
   20 \