fix: useTimeout文档中API处的delay属性的类型标注 (#2439)

Author: OweQian

packages/hooks/src/useTimeout/index.en-US.md

@@ -19,7 +19,7 @@ A hook that handles the `setTimeout` timer function.
 ```typescript
 useTimeout(
   fn: () => void,
-  delay?: number | null
+  delay?: number | undefined
 ): fn: () => void;
 ```
 

packages/hooks/src/useTimeout/index.zh-CN.md

@@ -19,7 +19,7 @@ nav:
 ```typescript
 useTimeout(
   fn: () => void,
-  delay?: number | null
+  delay?: number | undefined
 ): fn: () => void;
 ```