Travis CI: Test on Python 3.9 release candidate 2

.travis.yml

@@ -1,45 +1,36 @@
+os: linux
+dist: xenial
 language: python
 python:
-  - "2.6"
   - "2.7"
-  - "3.2"
-  - "3.3"
-  - "3.4"
   - "3.5"
   - "3.6"
+  - "3.7"
+  - "3.8"
+  - "3.9-dev"
   - "pypy"
   - "pypy3"
-dist: trusty
 env:
   - YTDL_TEST_SET=core
   - YTDL_TEST_SET=download
 jobs:
   include:
-    - python: 3.7
-      dist: xenial
-      env: YTDL_TEST_SET=core
-    - python: 3.7
-      dist: xenial
-      env: YTDL_TEST_SET=download
-    - python: 3.8
-      dist: xenial
-      env: YTDL_TEST_SET=core
-    - python: 3.8
-      dist: xenial
-      env: YTDL_TEST_SET=download
-    - python: 3.8-dev
-      dist: xenial
-      env: YTDL_TEST_SET=core
-    - python: 3.8-dev
-      dist: xenial
-      env: YTDL_TEST_SET=download
-    - env: JYTHON=true; YTDL_TEST_SET=core
-    - env: JYTHON=true; YTDL_TEST_SET=download
     - name: flake8
       python: 3.8
-      dist: xenial
       install: pip install flake8
       script: flake8 .
+    - python: 2.6  # test end of life Python version on end of life Trusty
+      dist: trusty
+    - python: 3.2
+      dist: trusty
+    - python: 3,3
+      dist: trusty
+    - python: 3.4
+      dist: trusty
+    - env: JYTHON=true; YTDL_TEST_SET=core
+      dist: trusty
+    - env: JYTHON=true; YTDL_TEST_SET=download
+      dist: trusty
   fast_finish: true
   allow_failures:
     - env: YTDL_TEST_SET=download