fix comment typo

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

go/vt/discovery/tablet_health_check.go

@@ -73,7 +73,7 @@ type tabletHealthCheck struct {
 	// LastError is the error we last saw when trying to get the
 	// tablet's healthcheck.
 	LastError error
-	// Timestamp is time time the healthcheck data was produced.
+	// Timestamp is represents the time the healthcheck data was produced.
 	Timestamp *vttime.Time
 	// possibly delete both these
 	loggedServingState    bool