Add missing dependency.

Dockerfile

@@ -8,7 +8,7 @@ RUN apt-get -y update && \
         git vim parted \
         quilt coreutils qemu-user-static debootstrap zerofree zip dosfstools \
         libarchive-tools libcap2-bin rsync grep udev xz-utils curl xxd file kmod bc\
-        binfmt-support ca-certificates qemu-utils kpartx \
+        binfmt-support ca-certificates qemu-utils kpartx util-linux \
     && rm -rf /var/lib/apt/lists/*
 
 COPY . /pi-gen/

depends

@@ -19,3 +19,4 @@ lsmod:kmod
 bc
 qemu-nbd:qemu-utils
 kpartx
+util-linux