OSB-45: fixing syntax for the docker registry

LCU/Maintenance/Docker/Jenkinsfile

@@ -15,7 +15,7 @@ pipeline {
                 echo 'building tag ${env.DOCKER_TAG}'
                 
                 script {
-                    withDockerRegistry("nexus.cep4.control.lofar:18081", "nexus"){
+                    withDockerRegistry(url:"nexus.cep4.control.lofar:18081", credentialsId:"nexus"){
                         dir ('LCU/Maintenance/Docker/BaseMaintenance/'){
                             docker.build "lofar-maintenance-base:${DOCKER_TAG}"
                         }