[formats] Rename variable 'data' to 'item'

This makes the intend of the variable more clear and is now
coherent with all Bridges

formats/JsonFormat.php

@@ -7,9 +7,9 @@ class JsonFormat extends FormatAbstract{
 
     public function stringify(){
         // FIXME : sometime content can be null, transform to empty string
-        $datas = $this->getItems();
+        $items = $this->getItems();
 
-        return json_encode($datas, JSON_PRETTY_PRINT);
+        return json_encode($items, JSON_PRETTY_PRINT);
     }
 
     public function display(){