Fix compatibility with Go < 1.5
Fix compatibility with Go < 1.5

byo/restic,ar-jan/restic,jayme-github/restic,ar-jan/restic,ckemper67/restic,bchapuis/restic,middelink/restic,kurin/restic,howeyc/restic,stuertz/restic,arithmetric/restic,kurin/restic,mappu/restic,restic/restic,middelink/restic,episource/restic,byo/restic,fawick/restic,fawick/restic,jayme-github/restic,restic/restic,stuertz/restic