travis: Update MariaDB download URLs.
travis: Update MariaDB download URLs.

Fixes recent Travis build errors.

mattharden/vitess,sougou/vitess,rnavarro/vitess,pivanof/vitess,vitessio/vitess,mahak/vitess,pivanof/vitess,alainjobart/vitess,tinyspeck/vitess,sougou/vitess,sougou/vitess,alainjobart/vitess,davygeek/vitess,alainjobart/vitess,tinyspeck/vitess,rnavarro/vitess,HubSpot/vitess,tirsen/vitess,davygeek/vitess,tirsen/vitess,enisoc/vitess,tinyspeck/vitess,mahak/vitess,tinyspeck/vitess,mahak/vitess,mahak/vitess,vitessio/vitess,alainjobart/vitess,alainjobart/vitess,mattharden/vitess,mattharden/vitess,HubSpot/vitess,dcadevil/vitess,HubSpot/vitess,enisoc/vitess,sougou/vitess,applift/vitess,mattharden/vitess,enisoc/vitess,alainjobart/vitess,HubSpot/vitess,tirsen/vitess,davygeek/vitess,sougou/vitess,enisoc/vitess,rnavarro/vitess,sougou/vitess,tirsen/vitess,tirsen/vitess,pivanof/vitess,mahak/vitess,pivanof/vitess,applift/vitess,enisoc/vitess,alainjobart/vitess,dcadevil/vitess,enisoc/vitess,mattharden/vitess,pivanof/vitess,pivanof/vitess,tinyspeck/vitess,rnavarro/vitess,vitessio/vitess,vitessio/vitess,applift/vitess,dcadevil/vitess,applift/vitess,dcadevil/vitess,sougou/vitess,davygeek/vitess,mahak/vitess,tirsen/vitess,applift/vitess,davygeek/vitess,vitessio/vitess,applift/vitess,applift/vitess,tinyspeck/vitess,mattharden/vitess,enisoc/vitess,mattharden/vitess,HubSpot/vitess,tirsen/vitess,tirsen/vitess,HubSpot/vitess,HubSpot/vitess,davygeek/vitess,rnavarro/vitess,mahak/vitess,vitessio/vitess,mattharden/vitess,rnavarro/vitess,rnavarro/vitess,vitessio/vitess,sougou/vitess,mattharden/vitess,applift/vitess,dcadevil/vitess,pivanof/vitess,alainjobart/vitess,mattharden/vitess,davygeek/vitess,HubSpot/vitess,applift/vitess,applift/vitess,vitessio/vitess,dcadevil/vitess,rnavarro/vitess,dcadevil/vitess,mahak/vitess,pivanof/vitess,rnavarro/vitess,tinyspeck/vitess,pivanof/vitess,tirsen/vitess