Update hook_civicrm_contact_get_displayname.md

Fix typo

docs/hooks/hook_civicrm_contact_get_displayname.md

@@ -16,7 +16,7 @@ don't want to store this in the database.
 
 ## Parameters
 
--   &$disply_name - the current display name, you can change the
+-   &$display_name - the current display name, you can change the
     display name by changing the contents of this parameter
 -   $contactId - Contact ID
 -   $objContact - The contact BAO
@@ -31,4 +31,4 @@ Below an example of showing the contact ID after the display name
 
     function myextension_civicrm_contact_get_displayname(&$display_name, $contactId, $objContact) {
         $display_name = $display_name . ' - '.$contactId;
-    }
+    }
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