Add v1 to metrics API endpoint

Fixes #1399

This versions the prometheus metrics API so we can manage backwards
incompatible changes in the future more easily.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

server/server.go

@@ -136,7 +136,7 @@ func (s *Server) ServeGRPC(l net.Listener) error {
 // ServeMetrics provides a prometheus endpoint for exposing metrics
 func (s *Server) ServeMetrics(l net.Listener) error {
 	m := http.NewServeMux()
-	m.Handle("/metrics", metrics.Handler())
+	m.Handle("/v1/metrics", metrics.Handler())
 	return trapClosedConnErr(http.Serve(l, m))
 }