Fix agent definition.
diff --git a/Jenkinsfile b/Jenkinsfile
index a3f9e9d..3d0b600 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -1,5 +1,7 @@
 pipeline {
-    agent 'ubuntu'
+    agent {
+        label: 'ubuntu'
+    }
 
     stages {
         stage('Build') {