Fix travis cache (#194)
Fix travis cache (#194)

Use Travis caching system to avoid having to download / compile CMake and SFML everytime
Mizugola/ObEngine,Zarakichi/ObEngine,Zarakichi/ObEngine,Mizugola/MeltingSagaEngine,Zarakichi/ObEngine,Mizugola/MeltingSagaEngine,Sygmei/ObEngine,Mizugola/MeltingSaga,Mizugola/MeltingSaga,Mizugola/ObEngine,Sygmei/ObEngine