fix vertical swipe navigation not blocking page scrolling in embedded decks

js/reveal.js

@@ -1446,6 +1446,9 @@ export default function( revealElement, options ) {
 		let currentHorizontalSlide = horizontalSlides[ indexh ],
 			currentVerticalSlides = currentHorizontalSlide.querySelectorAll( 'section' );
 
+		// Indicate when we're on a vertical slide
+		revealElement.classList.toggle( 'is-vertical-slide', currentVerticalSlides.length > 1 );
+
 		// Store references to the previous and current slides
 		currentSlide = currentVerticalSlides[ indexv ] || currentHorizontalSlide;