Html email sending as html

Question

So I have these header codes

 $headers = array(
            'MIME-Version:1.0',
            'Content-type: text/html; charset=iso-8859-1',
            'From: Mysterious Islands <no-reply@mysterious-islands.com>',
            'X-Mailer:PHP/' . phpversion(),
        );
        mail($email, 'Account Activation', $message, implode("\r\n", $headers

));

And I have tried removing the \r and the email is still being sent in plain text, what am I doing wrong