Update .travis.yml
Update .travis.yml

Update osx_image to xcode8.
tad-iizuka/swift-sdk,tad-iizuka/swift-sdk,tad-iizuka/swift-sdk,watson-developer-cloud/ios-sdk,tad-iizuka/swift-sdk,watson-developer-cloud/ios-sdk,watson-developer-cloud/ios-sdk,watson-developer-cloud/ios-sdk,tad-iizuka/swift-sdk,watson-developer-cloud/ios-sdk