Do not run travis on backport branches

backporting[bot] · 3nids · commit 4ce3f953ac34 · 2019-03-04T13:39:38.000+01:00
We only need to run them on the pull request, not on the push
diff --git a/.travis.yml b/.travis.yml
@@ -9,6 +9,7 @@ cache:
   directories:
     - ${HOME}/.ccache
   timeout: 1000
+if: branch !~ /^backport-\d+-on-/
 
 env:
   global:
