In the app's exports, I've added InterfaceSupplier (as UplSupplierImport). I'm having a problem with "Array to string conversion" once more. This is the new InterfaceSupplier that I've added to my app/export under the name UplSupplierImport. Because the new code for the controller was the same as your previous code:
class InterfaceSupplier implements ToArray
{
    public function array(array $row)
    {
        return [
            'nomorUrut' => $row[0],
            'namaSupplier' => $row[1],
            'singkatanSupplier' => $row[2],
            'tipeSupplier' => $row[3],
            'alamatSupplier' => $row[4],
            'kodePosSupplier' => $row[5],
            'noTelpSupplier' => $row[6],
            'noFax' => $row[7],
            'emailSupplier' => $row[8],
            'contakSupplier' => $row[9],
            'hp' => $row[10],
        ];
    }
}
and this the controller code:
public function postImport(Request $request)
{
    $path = $request->file('file')->getRealPath();
    $insert_data = Excel::toArray(new InterfaceSupplier(), $path);
    if(!empty($insert_data))
    {
        DB::table('uplSupplier')->insert($insert_data);
    }
    return back()->with('success', 'Excel Data Imported successfully.');
}