Remove redundant word in Possible Mistakes section

2-ui/2-events/01-introduction-browser-events/article.md

@@ -160,7 +160,7 @@ button.onclick = sayThanks;
 button.onclick = sayThanks();
 ```
 
-If we add parentheses, then `sayThanks()` becomes is a function call. So the last line actually takes the *result* of the function execution, that is `undefined` (as the function returns nothing), and assigns it to `onclick`. That doesn't work.
+If we add parentheses, then `sayThanks()` becomes a function call. So the last line actually takes the *result* of the function execution, that is `undefined` (as the function returns nothing), and assigns it to `onclick`. That doesn't work.
 
 ...On the other hand, in the markup we do need the parentheses: