CI: Use master branch for demo.bitmask.net deploy

Commit 55b784f2 fixed this for mail.bitmask.net, but
not for demo.bitmask.net. See
55b784f2

This fixes #8843.

tests/platform-ci/ci-build.sh

@@ -238,7 +238,7 @@ case "$CI_JOB_NAME" in
     ;;
   demo.bitmask.net)
     TAG='demovpn'
-    run bitmask ssh://gitolite@leap.se/bitmask
+    run bitmask ssh://gitolite@leap.se/bitmask master
     ;;
   deploy_test*)
     build_from_scratch