Silence error during purge of unneeded packages

bootstrap.sh

@@ -17,6 +17,8 @@ debootstrap \
     --no-merged-usr \
     --variant=minbase jessie $rootfs
 
+mount -t devpts devpts $rootfs/dev/pts
+
 chroot $rootfs apt-mark auto '.*' \
        | sed '/not installed/d'
 chroot $rootfs apt-mark manual devuan-keyring
@@ -30,3 +32,5 @@ for script in $(ls $rootfs/$bindir); do
 done
 
 chroot $rootfs apt-get --purge autoremove -q -y
+
+umount $rootfs/dev/pts