Fix CellValueFormatter for numeric values

The value passed into the format() function is coming from an XML file and has never been coerced.
Therefore, when checking is_int($value), the check always returns false - because it's a string.
Changing the check fixes the issue and Spout now correctly parses large numbers.

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

@@ -169,7 +169,8 @@ class CellValueFormatter
         if ($shouldFormatAsDate) {
             return $this->formatExcelTimestampValue(floatval($nodeValue));
         } else {
-            return is_int($nodeValue) ? intval($nodeValue) : floatval($nodeValue);
+            $nodeIntValue = intval($nodeValue);
+            return ($nodeIntValue == $nodeValue) ? $nodeIntValue : floatval($nodeValue);
         }
     }