Update icinga2_check_command_definition.conf

small error in icinga2 conf definition, --key_metricS does not exist --key_metric does.

contrib/icinga2_check_command_definition.conf

@@ -97,8 +97,8 @@ object CheckCommand "http_json" {
 			value = "$http_json_key_not_equals_critical$"
 			description = "Checks equality of these keys and values (key[>alias],value key2,value2) to determine status. Multiple key values can be delimited with colon (key,value1:value2). Return critical if equality check succeeds."
 		}
-		"--key_metrics" = {
-			value = "$http_json_key_metrics$"
+		"--key_metric" = {
+			value = "$http_json_key_metric$"
 			description = "Gathers the values of these keys"
 		}
 	}