Travis: Disable OSX and iOS temporarily

They haven't been updated yet for GLES3 support, so they will fail
all the time.

.travis.yml

@@ -11,8 +11,8 @@ os:
   - osx
 
 env:
-  - GODOT_TARGET=iphone
-  - GODOT_TARGET=osx
+  #- GODOT_TARGET=iphone
+  #- GODOT_TARGET=osx
   - GODOT_TARGET=x11
   #- GODOT_TARGET=android
   - GODOT_TARGET=windows