Update vendor.json with the `promhttp` package and a newer `prometheus` package.
Update vendor.json with the `promhttp` package and a newer `prometheus`
package.

Signed-off-by: Maggie Zhou <826b1579432fb3d92c18d0aaf5c045d46c2ddd46@slack-corp.com>

tinyspeck/vitess,enisoc/vitess,tinyspeck/vitess,dcadevil/vitess,alainjobart/vitess,HubSpot/vitess,alainjobart/vitess,HubSpot/vitess,mahak/vitess,davygeek/vitess,vitessio/vitess,vitessio/vitess,tinyspeck/vitess,tinyspeck/vitess,enisoc/vitess,mahak/vitess,davygeek/vitess,tinyspeck/vitess,alainjobart/vitess,davygeek/vitess,mahak/vitess,tinyspeck/vitess,enisoc/vitess,HubSpot/vitess,mahak/vitess,vitessio/vitess,vitessio/vitess,HubSpot/vitess,davygeek/vitess,davygeek/vitess,alainjobart/vitess,dcadevil/vitess,vitessio/vitess,vitessio/vitess,davygeek/vitess,vitessio/vitess,mahak/vitess,enisoc/vitess,mahak/vitess,HubSpot/vitess,dcadevil/vitess,enisoc/vitess,dcadevil/vitess,enisoc/vitess,HubSpot/vitess,alainjobart/vitess,mahak/vitess,alainjobart/vitess,dcadevil/vitess,tinyspeck/vitess,vitessio/vitess,davygeek/vitess,dcadevil/vitess,enisoc/vitess,alainjobart/vitess,mahak/vitess,dcadevil/vitess,HubSpot/vitess,alainjobart/vitess,HubSpot/vitess