Fix typo in Jenkinsfile

Change-Id: I6626238bd246af8ae40499ad285e9e9dbfbe34df
diff --git a/Jenkinsfile b/Jenkinsfile
index 625b4bc..ce609b7 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -48,7 +48,7 @@
         it =~ /^${osImageForRegex}-/
     }
     // dont cleanup non timestamp images
-    return imageToClean.findAll { it ->
+    return imagesToClean.findAll { it ->
         it =~ /${osImageForRegex}-x(64|32)-\d+${imageTypeForRegex}/
     }
 }