ci(travis): ubuntu upgrade from 16 to 18 & 20

Author: litnialex

.travis.yml

@@ -59,7 +59,8 @@ jobs:
     # Make sure the instances listed below match up with
     # the `platforms` defined in `kitchen.yml`
     - env: INSTANCE=default-debian-10-master-py3
-    # - env: INSTANCE=default-ubuntu-1804-master-py3
+    - env: INSTANCE=default-ubuntu-2004-master-py3
+    - env: INSTANCE=default-ubuntu-1804-master-py3
     # - env: INSTANCE=default-centos-8-master-py3
     # - env: INSTANCE=default-fedora-31-master-py3
     # - env: INSTANCE=default-opensuse-leap-151-master-py3
@@ -75,7 +76,6 @@ jobs:
     # - env: INSTANCE=default-arch-base-latest-2019-2-py2
     # - env: INSTANCE=default-fedora-30-2018-3-py3
     # - env: INSTANCE=default-debian-9-2018-3-py2
-    - env: INSTANCE=default-ubuntu-1604-2018-3-py2
     # - env: INSTANCE=default-centos-7-2018-3-py2
     - env: INSTANCE=default-opensuse-leap-151-2018-3-py2
     # - env: INSTANCE=default-amazonlinux-1-2018-3-py2