chore: test xcode9.3 for UI tests

Author: DimitarTodorov

.travis.yml

@@ -72,7 +72,7 @@ matrix:
       jdk: oraclejdk8
       env: 
         - iOS="UnitTests"
-      osx_image: xcode8.3 # Can't run the tests using the latest xcode for now
+      osx_image: xcode9.3 # Can't run the tests using the latest xcode for now
       before_script:
         - cd demo && tns platform add ios@next
       script: