Stop `make` if working tree does not have git repository
Stop `make` if working tree does not have git repository

Fix https://github.com/jpsim/SourceKitten/issues/262
See also: https://github.com/jspahrsummers/objc-build-scripts/issues/13

firebase/SwiftLint,Johnykutty/SwiftLint,firebase/SwiftLint,jeffreybergier/SwiftLint,Johnykutty/SwiftLint,Johnykutty/SwiftLint,lyft/SwiftLint,lyft/SwiftLint,lyft/SwiftLint,realm/SwiftLint,firebase/SwiftLint,victorpimentel/SwiftLint,lyft/SwiftLint,firebase/SwiftLint,realm/SwiftLint,jeffreybergier/SwiftLint,realm/SwiftLint,jeffreybergier/SwiftLint,Johnykutty/SwiftLint,victorpimentel/SwiftLint,realm/SwiftLint,victorpimentel/SwiftLint,victorpimentel/SwiftLint,jeffreybergier/SwiftLint