Update Nexus credentials property names and Jenkins pipeline for publishing

Jenkinsfile

@@ -8,7 +8,12 @@ pipeline {
         }
         stage('Publish to Maven') {
             steps {
-                sh './gradlew publish -PalttdSnapshotUsername=$NEXUS_CREDS_USR -PalttdSnapshotPassword=$NEXUS_CREDS_PSW'
+                withCredentials([usernameColonPassword(credentialsId: 'alttd-publish-user', variable: 'USERPASS')]) {
+                sh '''
+                  set +x
+                  sh './gradlew publish -PalttdDevPublishUser=publish -PalttdDevPublishPass=$USERPASS'
+                '''
+                }
             }
         }
         stage('Archive') {