Code review changes

tests/Spout/Writer/XLSX/WriterPerfTest.php

@@ -135,7 +135,7 @@ class WriterPerfTest extends TestCase
         copy($filePath, $tmpFile);
 
         // Get the last 200 characters
-        $lastCharacters = `tail -c $numCharacters $tmpFile`;
+        $lastCharacters = shell_exec("tail -c $numCharacters $tmpFile");
 
         // remove the temporary file
         unlink($tmpFile);