Travis: allow_failures for FFmpeg 3.2

Author: ferdnyc

.travis.yml

@@ -32,8 +32,12 @@ addons:
     - curl
 
 jobs:
-  include:
 
+  # The FFmpeg 3.2 backport PPA has gone missing
+  allow_failures:
+    - name: "FFmpeg 3.2 GCC (Ubuntu 16.04 Xenial)"
+
+  include:
     - name: "Coverage + FFmpeg 3.4 GCC (Ubuntu 18.04 Bionic)"
       env:
         - BUILD_VERSION=coverage_ffmpeg34