update .travis.yml to xcode 9.4

NSProgrammer · web-flow · commit 8ab45ce6a3da · 2018-08-10T16:57:11.000-07:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,4 +1,4 @@
-osx_image: xcode9.3
+osx_image: xcode9.4
 language: objective-c
 script:
 # iOS Static Lib
