travis: run debsources-update more verbosely
travis: run debsources-update more verbosely

this is both to ease debugging when needed, and to avoid triggering travis "the
process is doing nothing" alert

Debian/debsources,clemux/debsources,clemux/debsources,Debian/debsources,Debian/debsources,zacchiro/debsources,zacchiro/debsources,vivekanand1101/debsources,zacchiro/debsources,oorestisime/debsources,clemux/debsources,oorestisime/debsources,matthieucan/debsources,oorestisime/debsources,devoxel/debsources,devoxel/debsources,matthieucan/debsources,zacchiro/debsources,Debian/debsources,matthieucan/debsources,clemux/debsources,matthieucan/debsources,vivekanand1101/debsources,vivekanand1101/debsources,devoxel/debsources,oorestisime/debsources,oorestisime/debsources,clemux/debsources,matthieucan/debsources,vivekanand1101/debsources,devoxel/debsources,vivekanand1101/debsources,Debian/debsources,devoxel/debsources,zacchiro/debsources