travis: switch to xenial, update distributions

QubesOS/qubes-issues#4613

.travis.yml

@@ -1,5 +1,5 @@
 sudo: required
-dist: trusty
+dist: xenial
 language: python
 python:
   - '2.7'
@@ -24,14 +24,16 @@ jobs:
   include:
     - env: DIST_DOM0=fc25 USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
       python: '3.5'
-    - env: DISTS_VM=fc24 USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
+    - env: DISTS_VM=fc29 USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
       python: '3.5'
-    - env: DISTS_VM=fc25 USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
+    - env: DISTS_VM=fc30 USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
       python: '3.5'
     - env: DISTS_VM=jessie USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
       python: '3.4'
     - env: DISTS_VM=stretch USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
       python: '3.5'
+    - env: DISTS_VM=buster USE_QUBES_REPO_VERSION=4.0 USE_QUBES_REPO_TESTING=1 TESTS_ONLY=
+      python: '3.5'
     - stage: deploy
       python: '3.5'
       env: DIST_DOM0=fc25 TESTS_ONLY=