updated module attributes

gce-create-instances.yml

diff --git a/gce-create-instances.yml b/gce-create-instances.yml
index 966786d..05e7b4d 100644
--- a/gce-create-instances.yml
+++ b/gce-create-instances.yml
@@ -28,6 +28,7 @@
       credentials_file: '{{ credentials_file }}'
       state: present
       tags: "{{ default_firewall_tags }}"
+      metadata: '{}'
     register: gce
 
 #  - name: Create firewall rule