Convert escapers to singletons (#239)

src/Spout/Reader/XLSX/Helper/SheetHelper.php

@@ -87,7 +87,7 @@ class SheetHelper
         $escapedSheetName = $xmlReaderOnSheetNode->getAttribute('name');
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
         $sheetName = $escaper->unescape($escapedSheetName);
 
         $sheetDataXMLFilePath = $this->getSheetDataXMLFilePathForSheetId($sheetId);