debian/control: Set Standards-Version to 3.9.7

We do not follow the recommendation with regards to placement
of documentation in apt-doc, as we install in apt-doc, but
it's only a recommendation and I don't want think we should
move them.

debian/control

@@ -4,7 +4,7 @@ Priority: important
 Maintainer: APT Development Team <deity@lists.debian.org>
 Uploaders: Michael Vogt <mvo@debian.org>,
  Julian Andres Klode <jak@debian.org>
-Standards-Version: 3.9.6
+Standards-Version: 3.9.7
 Build-Depends: dpkg-dev (>= 1.17.14), debhelper (>= 9.20141010), libdb-dev,
  gettext (>= 0.12), libcurl4-gnutls-dev (>= 7.19.4~),
  zlib1g-dev, libbz2-dev, liblzma-dev, liblz4-dev (>= 0.0~r126),