prometheus: fix 'in_flight' metric name

templates/server/prometheus.gotmpl

@@ -27,7 +27,7 @@
 
     {{ camelize .Name }}HandlerInFlight = prometheus.NewGauge(
         prometheus.GaugeOpts{
-            Name: "orus_api_handler_in_flignts",
+            Name: "orus_api_handler_in_flight",
             Help: "The number of handlers currently running.",
             ConstLabels: map[string]string{
                 "service": "{{.Name}}",