Consistently use event prefix for calendar and list templates

Retain backwards compatibility

admin/post-types/calendar.php

@@ -62,7 +62,7 @@ function sportspress_calendar_shortcode_meta( $post ) {
 	<p class="howto">
 		<?php _e( 'Copy this code and paste it into your post, page or text widget content.', 'sportspress' ); ?>
 	</p>
-	<p><input type="text" value="[events-<?php echo $the_format; ?> <?php echo $post->ID; ?>]" readonly="readonly" class="wp-ui-text-highlight code"></p>
+	<p><input type="text" value="[event-<?php echo $the_format; ?> <?php echo $post->ID; ?>]" readonly="readonly" class="wp-ui-text-highlight code"></p>
 	<?php
 }