CRM-12345 Fix typo in MembershipType.tpl.

----------------------------------------
* CRM-12345: typo in text      templates/CRM/Member/Form/MembershipType.tpl
  http://issues.civicrm.org/jira/browse/CRM-12345
Merge pull request #418 from davecivicrm/CRM-12345

CRM-12345 Fix typo in MembershipType.tpl.