Issue 6560 - fix malformed updates.json

sitescripts/extensions/template/gecko.json

 {
   "addons": {
   {%- for extension in extensions %}
     "{{ extension.extensionID }}": {
       "updates": [
         {
           "version": "{{ extension.version }}",
           "update_link": "{{ extension.update_link }}",
           "applications": {
             "gecko": { "strict_min_version": "{{ extension.min_version }}" }
           }
         }
       ]
-    }

[kzar, 2018/04/06 09:55:49]

If there are multiple extensions won't we be missing the commas between the
entries here?

[tlucas, 2018/04/06 10:08:32]

Good point, fixed it.

+    }{% if not loop.last %},{% endif %}
   {%- endfor %}
   }
 }