Update Nexus credentials property names and adjust Jenkins pipeline for Gradle build

Jenkinsfile

@@ -3,7 +3,12 @@ pipeline {
     stages {
         stage('Gradle') {
             steps {
-                sh './gradlew build -PalttdSnapshotUsername=$NEXUS_CREDS_USR -PalttdSnapshotPassword=$NEXUS_CREDS_PSW'
+                withCredentials([usernameColonPassword(credentialsId: 'alttd-publish-user', variable: 'USERPASS')]) {
+                sh '''
+                  set +x
+                  sh './gradlew build -PalttdDevPublishUser=publish -PalttdDevPublishPass=$USERPASS'
+                '''
+                }
             }
         }
         stage('Publish to Maven') {