Use computed value of formula cells (#342)

Introduced by openspout/openspout#169

src/Importable.php

@@ -4,6 +4,7 @@
 
 use Illuminate\Support\Collection;
 use Illuminate\Support\Str;
+use OpenSpout\Common\Entity\Cell;
 use OpenSpout\Reader\SheetInterface;
 use OpenSpout\Writer\Common\AbstractOptions;
 
@@ -148,7 +149,13 @@ private function importSheet(SheetInterface $sheet, callable $callback = null)
         $count_header = 0;
 
         foreach ($sheet->getRowIterator() as $k => $rowAsObject) {
-            $row = $rowAsObject->toArray();
+            $row = array_map(function (Cell $cell) {
+                return match (true) {
+                    $cell instanceof Cell\FormulaCell => $cell->getComputedValue(),
+                    default                           => $cell->getValue(),
+                };
+            }, $rowAsObject->getCells());
+
             if ($k >= $this->start_row) {
                 if ($this->with_header) {
                     if ($k == $this->start_row) {