* Upgrade iOS project and related dependencies to Swift 5
* bump travis image to xcode10.2
* bump iphonesimulator to 12.2
* print out carthage version during test setup
* fix ios version in xcbuild test -destination
* Remove problematic Swift 5 branching logic in `Component`, fixes test
Because didComplete is added at the end of the Workflow Rx side-effect, if a Workflow is forked, multiple Rx chains with the side-effect are created and subscribed to. This means the didComplete is invoked duplicately.
Fixes#211