Bail out if xcodebuild -list hangs for ≥ 4 seconds
Bail out if xcodebuild -list hangs for ≥ 4 seconds

Works around #183.

abbeycode/Carthage,erichoracek/Carthage,flovilmart/Carthage,0xced/Carthage,erichoracek/Carthage,NachoSoto/Carthage,0xced/Carthage,NachoSoto/Carthage,0xced/Carthage,NachoSoto/Carthage,flovilmart/Carthage,abbeycode/Carthage,flovilmart/Carthage,erichoracek/Carthage,abbeycode/Carthage,erichoracek/Carthage,abbeycode/Carthage