fix typo in css-snappoints doc

Author: mikehenrty

css-snappoints/Overview.src.html

@@ -64,7 +64,7 @@ <h2 id="examples">Motivating Examples</h2>
         Using mandatory snap points,
         scrolling will always complete with a snap point aligned to the edge of the <a>scroll container's</a> visual viewport.
         By aligning a snap point at the edge of each image,
-        this creates a photo viewer were users can scroll through the images one at a time.
+        this creates a photo viewer where users can scroll through the images one at a time.
 
         <pre>
         img {