Fix build for < go1.7
Fix build for < go1.7

yonjah/rclone,ncw/rclone,olihey/rclone,arcimboldo/rclone,arcimboldo/rclone,yonjah/rclone,ncw/rclone,B4dM4n/rclone,jackschmidt/rclone,jackschmidt/rclone,B4dM4n/rclone,arcimboldo/rclone,jackschmidt/rclone,seuffert/rclone,olihey/rclone,kynikos/rclone,kynikos/rclone,ncw/rclone,jackschmidt/rclone,yonjah/rclone,kynikos/rclone,olihey/rclone,kynikos/rclone,olihey/rclone,yonjah/rclone,seuffert/rclone,B4dM4n/rclone,arcimboldo/rclone,seuffert/rclone,ncw/rclone,B4dM4n/rclone,seuffert/rclone