validateSubTypeByEntity checks value instead of key (Fatal error after 4.7.7 upgrade)

We're experiencing an issue after updating to 4.7.7

We're hitting a fatal error in the method CRM_Core_BAO_CustomGroup::validateSubTypeByEntity
https://github.com/civicrm/civicrm-core/blob/6b85570b47e529d1d728e972ece3b95d9330009b/CRM/Core/BAO/CustomGroup.php#L655

This function is looking for the entity type in an array:
if ($entityType != 'Contact' && !in_array($entityType, $contactTypes['values'])) {

as a value when it should be looking for the key.

In our case we have 'Organisation' not 'Organization' so the array looks like:

Organization => Organisation

So in_array isn't working.

PR forthcoming to use array_key_exists instead