breaking: bump xcode requirement to 11.5
diff --git a/.travis.yml b/.travis.yml
index 20b080d..015b6a9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -19,7 +19,7 @@
 
 _ios: &_ios
   os: osx
-  osx_image: xcode10.3
+  osx_image: xcode11.5
 
 _android: &_android
   language: android