src/UploadHandlerBuilder.php
public function allowMimeTypes($mimeTypes)
    {
        if (!is_array($mimeTypes)) {
            $mimeTypes = [$mimeTypes];
        }
        $this->constraints[] = new MimeTypeConstraint($mimeTypes);
        return $this;
    }
public function allowMimeTypes($mimeTypes)
    {
        if (!is_array($mimeTypes)) {
            $mimeTypes = [$mimeTypes];
        }
        $this->constraints[] = new MimeTypeConstraint($mimeTypes);
        return $this;
    }
Set allowed mime types.

@param array|string $mimeTypes
@return $this