Update Travis CI settings to only build master branch

.travis.yml

@@ -1,5 +1,8 @@
 language: objective-c
 osx_image: xcode611
+branches:
+  only:
+    - master
 env:
 - LC_CTYPE=en_US.UTF-8 LANG=en_US.UTF-8
 before_install:
@@ -8,6 +11,6 @@ script:
 - set -o pipefail
 - xcodebuild -project Alamofire.xcodeproj -scheme "Alamofire iOS" -sdk iphonesimulator
   -destination "platform=iOS Simulator,name=iPhone 6" ONLY_ACTIVE_ARCH=NO  test | xcpretty -c
-- xcodebuild -project "iOS Example.xcodeproj" -scheme "iOS Example" -sdk iphonesimulator 
+- xcodebuild -project "iOS Example.xcodeproj" -scheme "iOS Example" -sdk iphonesimulator
   -destination "platform=iOS Simulator,name=iPhone 6" ONLY_ACTIVE_ARCH=YES build | xcpretty -c
 - pod lib lint --quick