Use Xcode11 image

SvenTiigi · SvenTiigi · commit de1efac91a0f · 2019-09-22T10:48:24.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -10,7 +10,7 @@ notifications:
     on_success: change
     on_failure: always
 
-osx_image: xcode10.2
+osx_image: xcode11
 language: swift
 
 before_script:
