prometheus hotfix (#670)

src/main/kotlin/io/emeraldpay/dshackle/monitoring/MonitoringSetup.kt

@@ -91,6 +91,7 @@ class MonitoringSetup(
         if (monitoringConfig.prometheus.enabled) {
             // use standard JVM server with a single thread blocking processing
             // prometheus is a single thread periodic call, no reason to setup anything complex
+            Thread {
                 var started = false
                 while (true) {
                     if (isTcpPortAvailable(monitoringConfig.prometheus.host, monitoringConfig.prometheus.port)) {
@@ -126,6 +127,7 @@ class MonitoringSetup(
                         Thread.sleep(1000)
                     }
                 }
+            }.start()
         }
     }
 }