Change label to `prod`

Target only the web host node in order to deploy.

undeployed/ci/jenkinsfile

@@ -1,7 +1,7 @@
 #!/usr/bin/env groovy
 
 pipeline {
-    agent { label 'linux' }
+    agent { label 'prod' }
     stages {
         stage('Intro') {
             steps {