sodium.ffi: add the year 2018 to the copyright notice
sodium.ffi: add the year 2018 to the copyright notice

AlexIljin/factor,tgunr/factor,AlexIljin/factor,factor/factor,mrjbq7/factor,bpollack/factor,tgunr/factor,bpollack/factor,mrjbq7/factor,tgunr/factor,bpollack/factor,AlexIljin/factor,mrjbq7/factor,mrjbq7/factor,factor/factor,mrjbq7/factor,factor/factor,factor/factor,bpollack/factor,AlexIljin/factor,tgunr/factor,factor/factor,factor/factor,tgunr/factor,AlexIljin/factor,AlexIljin/factor,bpollack/factor,bpollack/factor,tgunr/factor,AlexIljin/factor,bpollack/factor,mrjbq7/factor