Updating Debian control to gexiv2 0.5.0
Updating Debian control to gexiv2 0.5.0

This is technically not required for building Shotwell, but we
want to move automated packaging builds now and in the future
to newer versions.

jimbonator/shotwell,damianmoore/shotwell,polymeris/shotwell,polymeris/shotwell,damianmoore/shotwell,ritchiewilson/shotwell,abrauchli/shotwell,jimbonator/shotwell,abrauchli/shotwell,polymeris/shotwell,damianmoore/shotwell,abrauchli/shotwell,jimbonator/shotwell,ritchiewilson/shotwell,ritchiewilson/shotwell