Invalid Markup: No space between attributes

On lines 95-97 of subscribe-to-comments-reloaded.php:

<option value='none'" . ( ( get_option( 'subscribe_reloaded_default_subscription_type' ) === '0' ) ? "selected='selected'" : '' ) . ">" . __( "Don't subscribe", 'subscribe-reloaded' ) . "</option>
<option value='yes'" . ( ( get_option( 'subscribe_reloaded_default_subscription_type' ) === '1' ) ? "selected='selected'" : '' ) . ">" . __( "All", 'subscribe-reloaded' ) . "</option>
<option value='replies'" . ( ( get_option( 'subscribe_reloaded_default_subscription_type' ) === '2' ) ? "selected='selected'" : '' ) . ">" . __( "Replies to my comments", 'subscribe-reloaded' ) . "</option>

should be replaced with:

<option value='none'" . ( ( get_option( 'subscribe_reloaded_default_subscription_type' ) === '0' ) ? " selected='selected'" : '' ) . ">" . __( "Don't subscribe", 'subscribe-reloaded' ) . "</option>
<option value='yes'" . ( ( get_option( 'subscribe_reloaded_default_subscription_type' ) === '1' ) ? " selected='selected'" : '' ) . ">" . __( "All", 'subscribe-reloaded' ) . "</option>
<option value='replies'" . ( ( get_option( 'subscribe_reloaded_default_subscription_type' ) === '2' ) ? " selected='selected'" : '' ) . ">" . __( "Replies to my comments", 'subscribe-reloaded' ) . "</option>

to add a space between option attributes value and selected in order to avoid invalid HTML.

https://ww.wp.xz.cn/plugins/subscribe-to-comments-reloaded/