Travis CI: Bump macOS image for LeakSanitizer

With default image "xcode9.4" we'd get:
==89222==AddressSanitizer: detect_leaks is not supported on this platform.

diff --git a/.travis.yml b/.travis.yml
index 01dd26e7ffe9b4531eb8237883a84802460bfae5..3d4392344639518a8212fcfc424be2f0f76398f5 100644 (file)
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,6 +6,7 @@ os:
   - linux
   - osx
 dist: trusty
+osx_image: xcode11
 
 git:
   depth: 50