Fix checkout GitSCM syntax to properly check out a specific commit

Change-Id: I9aa3aecd63b41997d5c65b46b85488f4463b1e28
diff --git a/jjb/pipeline/docker-publish.groovy b/jjb/pipeline/docker-publish.groovy
index dce23f1..9b2e74b 100644
--- a/jjb/pipeline/docker-publish.groovy
+++ b/jjb/pipeline/docker-publish.groovy
@@ -25,10 +25,8 @@
       steps {
         checkout([
           $class: 'GitSCM',
-          userRemoteConfigs: [[
-            url: "${params.gitUrl}",
-            name: "${params.gitRef}",
-          ]],
+          userRemoteConfigs: [[ url: "${params.gitUrl}", ]],
+          branches: [[ name: "${params.gitRef}", ]],
           extensions: [
             [$class: 'WipeWorkspace'],
             [$class: 'RelativeTargetDirectory', relativeTargetDir: "${params.projectName}"],