Fix small typo in concurrent-mode-reference.md (#2533)

`MySlowList` "lag behind" => `MySlowList` "lags behind"

content/docs/concurrent-mode-reference.md

@@ -199,7 +199,7 @@ function App() {
  }
 ```
 
-This allows us to start showing the new text for the `input` immediately, which allows the webpage to feel responsive. Meanwhile, `MySlowList` "lag behind" for up to 2 seconds according to the `timeoutMs` before updating, allowing it to render with the current text in the background.
+This allows us to start showing the new text for the `input` immediately, which allows the webpage to feel responsive. Meanwhile, `MySlowList` "lags behind" for up to 2 seconds according to the `timeoutMs` before updating, allowing it to render with the current text in the background.
 
 **For an in-depth look at deferring values, you can read [Concurrent UI Patterns](/docs/concurrent-mode-patterns.html#deferring-a-value).**