[views] fix typo in dictionnary access

Fixes #5

cubicweb_prometheus/views.py

@@ -134,7 +134,7 @@
             if "time_routes" in PD_METRICS:
                 PD_METRICS["time_routes"].labels(route_name).inc(duration)
             if "slow_routes" in PD_METRICS and duration > SLOW_REQUEST_THRESHOLD:
-                PD_METRICS["slow_route"].labels(route_name).inc()
+                PD_METRICS["slow_routes"].labels(route_name).inc()
             if "http_requests" in PD_METRICS:
                 PD_METRICS["http_requests"].labels(
                     method=request.method,