travis: Upgrade brew packages
travis: Upgrade brew packages

Installed packages might be outdated by the time the build
runs, so we should update them.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Reviewed-by: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,crobinso/libvirt,nertpinx/libvirt,crobinso/libvirt,crobinso/libvirt,andreabolognani/libvirt,jardasgit/libvirt,zippy2/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,eskultety/libvirt,libvirt/libvirt,zippy2/libvirt,jardasgit/libvirt,libvirt/libvirt,zippy2/libvirt,fabianfreyer/libvirt,crobinso/libvirt,olafhering/libvirt,andreabolognani/libvirt,eskultety/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,eskultety/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,eskultety/libvirt,jardasgit/libvirt,jardasgit/libvirt,libvirt/libvirt,jardasgit/libvirt,jfehlig/libvirt,jfehlig/libvirt,zippy2/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,eskultety/libvirt,nertpinx/libvirt,olafhering/libvirt,olafhering/libvirt