Fix a typo in stacklight job definition

Change-Id: I559495889b476adae78da15eb2df6439537c298f
diff --git a/jenkins/client/job/stacklight/cookiecutter.yml b/jenkins/client/job/stacklight/cookiecutter.yml
index 0ef4b5b..fa97f29 100644
--- a/jenkins/client/job/stacklight/cookiecutter.yml
+++ b/jenkins/client/job/stacklight/cookiecutter.yml
@@ -25,7 +25,7 @@
               description: "ID of jenkins credentials for connecting to gerrit"
               default: "gerrit"
             COOKIECUTTER_TEMPLATE_CONTEXT_FILE:
-              type: choice
+              type: string
               description: "Context for cookiecutter template specified as filename"
               default: 'stacklight-openstack-ovs-core-pike'
             OPENSTACK_API_PROJECT: