Fix typo

Author: mhagander

template.jinja/membership/mail/expired.html

@@ -10,7 +10,7 @@
 registration fee your membership will be reactivated immediately.
 </p>
 
-{{ button("Rejoin " + orgname, sitebase + "/membership/") }}
+{{ button("Rejoin " + org_name, sitebase + "/membership/") }}
 
 <p>
 If you no longer wish to be a member of {{org_name}}, this