Update the Travis to use Xcode 12

dreampiggy · dreampiggy · commit 991680550eef · 2021-02-23T17:52:13.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,5 @@
 language: swift
-osx_image: xcode11.4
+osx_image: xcode12
 
 env:
   global:
