Update the version of the prometheus client library we have vendored so

that we can use true histograms rather than the old Summary type that
calculated quantiles on the client side.

Godeps/_workspace/src/github.com/prometheus/procfs/doc.go

@@ -22,7 +22,7 @@
 //    	"fmt"
 //    	"log"
 //
-//    	"github.com/prometheus/client_golang/procfs"
+//    	"github.com/prometheus/procfs"
 //    )
 //
 //    func main() {
@@ -31,7 +31,7 @@
 //    		log.Fatalf("could not get process: %s", err)
 //    	}
 //
-//    	stat, err := p.Stat()
+//    	stat, err := p.NewStat()
 //    	if err != nil {
 //    		log.Fatalf("could not get process stat: %s", err)
 //    	}