Crash instead of printing banner when called without a path to object definitions

[jhchabran]

I must have broken something, it panics without the path :

 (master) ~/go/src/github.com/openflylab/bridge$ sudo ./bridge -port 3000 uavobjectdefinition/
2015/06/28 15:20:32 Websocket server started on port 3000
^C (master) ~/go/src/github.com/openflylab/bridge$ sudo ./bridge -port 3000 
panic: runtime error: index out of range

goroutine 1 [running]:
runtime.panic(0x66da60, 0xb84657)
        /usr/lib/go/src/pkg/runtime/panic.c:266 +0xb6
main.main()
        /home/tech/go/src/github.com/openflylab/bridge/main.go:18 +0x29b

goroutine 3 [syscall]:
runtime.goexit()
        /usr/lib/go/src/pkg/runtime/proc.c:1394