Fix issue where CocoaPods is running actool

actool was introduced with Xcode 5, so this command is not available on
our VMs yet. Was adviced on Twitter
(https://twitter.com/alloy/status/393438997902819328) to make it a
no-op.
Merge pull request #157 from travis-ci/hh-fix-cocoapods-actool

Fix issue where CocoaPods is running actool