Add exportFormat method.

This PR is in relation with https://github.com/yajra/laravel-datatables-export package.

Author: jaydons

src/Html/Column.php

@@ -567,6 +567,20 @@ public function titleAttr($value)
         return $this;
     }
 
+    /**
+     * Set excel column format when exporting.
+     *
+     * @param string $format
+     * @return $this
+     * @see https://github.com/yajra/laravel-datatables-export
+     */
+    public function exportFormat($format)
+    {
+        $this->attributes['exportFormat'] = $format;
+
+        return $this;
+    }
+
     /**
      * @return array
      */