Backport PR #15851: ffmpeg is available on default ubuntu packages now.

jklymak · timhoffm · commit 022b5ebe1a8c · 2019-12-07T18:17:40.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -21,8 +21,6 @@ addons:
     paths:
     - result_images.tar.bz2
   apt:
-    sources:
-      - sourceline: ppa:jonathonf/ffmpeg-3
     packages:
       - cm-super
       - dvipng
