Update article.md

Author: leviding

2-ui/3-event-details/1-mouse-events-basics/article.md

@@ -50,7 +50,7 @@ Also we can see the `button` property that allows to detect the mouse button, it
 
 Click-related events always have the `button` property, which allows to get the exact mouse button.
 
-We usually don't use it for `click` and `contextmenu` events, because the former happens only on left-click, and the latter -- only on right-click. 
+We usually don't use it for `click` and `contextmenu` events, because the former happens only on left-click, and the latter -- only on right-click.
 
 From the other hand, `mousedown` and `mouseup` handlers we may need `event.button`, because these events trigger on any button, so `button` allows to distinguish between "right-mousedown" and "left-mousedown".