Update Xcode 7.2 on Travis CI

.travis.yml

@@ -1,10 +1,9 @@
 language: objective-c
-osx_image: xcode7.1
+osx_image: xcode7.2
 cache:
   directories:
     - Lib/vendor/bundle
 install:
-  - brew update && brew install carthage
   - "(cd Lib && bundle install --path=vendor/bundle --binstubs=vendor/bin)"
 before_script:
   - openssl aes-256-cbc -k "$ENCRYPTION_SECRET" -in ./Lib/Certificates/developer.p12.enc -d -a -out ./Lib/Certificates/developer.p12 || true