control: Bump Standards-Version

control: Bump Standards-Version

I have been through the upgrading checklist.

I came across two things which were mentioned but which I haven't
implemented:

 * nodoc build option.  It's not clear to me whether this is
   superseded by the nodocs build profile.  If we wanted to bootstrap
   using dgit, the build profile would probably be better.

 * using ${perl:Depends}.  I looked into this briefly and dh_perl
   doesn't seem to DTRT right now: it doesn't spot any of the modules
   we use.  I'm not sure why and have decided to punt on this for now.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>