Remove SwiftLint step from travis.yml and update image to Xcode 8.3

Author: freak4pc

.travis.yml

@@ -1,5 +1,5 @@
 language: objective-c
-osx_image: xcode7.3
+osx_image: xcode8.3
 rvm:
   - "2.3.1"
 
@@ -12,9 +12,6 @@ env:
     - OS=macos
     - OS=tvos
 
-before_install:
-  - brew install swiftlint
-
 install:
   - gem install bundler --no-doc --no-ri
   - bundle install --path="./.vendor/bundle"