ci: Bump ci macOS version (#254)

* use macOS 10.15

Author: KazuCocoa

ci-jobs/functional_test.yml

@@ -1,7 +1,7 @@
 # jobs for functional test
 parameters:
-  vmImage: 'macOS-10.14'
-  vmImageForIOS: 'macOS-10.14' # Not sure the reason, but macOS 10.14 instance raises no info.plist error
+  vmImage: 'macOS-10.15'
+  vmImageForIOS: 'macOS-10.15' # Not sure the reason, but macOS 10.14 instance raises no info.plist error
   xcodeForIOS: 11.3
   xcodeForTVOS: 11.3
   androidSDK: 29