Update all vendored code

[kkuehlz]

prometheus.NewProcessCollector now takes prometheus.ProcessCollectorOpts instead of a pid and a namespace. Passing PidFn as nil is equivalent to the old behavior. prometheus.UninstrumentedHandler is severely deprecated and now we just use promhttp.Handler,

[kkuehlz]

Also, I only included the vendor directory because that's what master does. Is there a reason we don't just include the vendor/vendor.json and anyone that checks out the repo just runs govendor sync?