Use new files API for file path inputs

[mattt]

Related to replicate/replicate-go#39

$ replicate run andreasjansson/blip-2 image=@/path/to/gg_bridge.jpeg
Prediction created: https://replicate.com/p/7uugy3zbbhhtkku4fctfu33gc4
processing 100% |████████████████████████████████████| (0/100, 0 it/hr)        
✅ Succeeded
"golden gate bridge"