Fix a typo (slab#2327)

docs/docs/modules/keyboard.md

@@ -209,6 +209,6 @@ var quill = new Quill('#editor', {
 ```
 
 
-### Peformance
+### Performance
 
 Like DOM events, Quill key bindings are blocking calls on every match, so it is a bad idea to have a very expensive handler for a very common key binding. Apply the same performance best practices as you would when attaching to common blocking DOM events, like `scroll` or `mousemove`.