Update events.md (vuejs#1446)

* Update events.md

* Tweak wording and grammar in key modifiers

Author: 01abhishekjain

src/v2/guide/events.md

@@ -295,7 +295,7 @@ For example:
 <div @click.ctrl="doSomething">Do something</div>
 ```
 
-<p class="tip">Note that modifier keys are different from regular keys and when used with `keyup` events, they have to be pressed when the event is emitted. In other words, `keyup.ctrl` will only trigger if you release a key while holding down `ctrl`. It won't trigger if you release the `ctrl` key alone.</p>
+<p class="tip">Note that modifier keys are different from regular keys and when used with `keyup` events, they have to be pressed when the event is emitted. In other words, `keyup.ctrl` will only trigger if you release a key while holding down `ctrl`. It won't trigger if you release the `ctrl` key alone. If you do want such behaviour, use the `keyCode` for `ctrl` instead: `keyup.17`.</p>
 
 ### `.exact` Modifier