Add python-sphinx to the build dependences

debian/control

@@ -4,7 +4,7 @@ Priority: extra
 Maintainer: Nikos Skalkotos <skalkoto@grnet.gr>
 Build-Depends: debhelper (>= 7.0.50~), automake, autotools-dev, kpartx,
  gdisk, eatmydata, mbr, curl, xmlstarlet, parted, libhivex-bin,
- libwin-hivex-perl, python, python-prctl, python-scapy
+ libwin-hivex-perl, python, python-prctl, python-scapy, python-sphinx
 Standards-Version: 3.9.4
 Homepage: https://code.grnet.gr/projects/snf-image
 Vcs-Git: git://code.grnet.gr/git/snf-image