📚 Doc: Fix static middleware CacheDuration data type typo (#3273)

docs/middleware/static.md

@@ -154,7 +154,7 @@ To define static routes using `Get`, append the wildcard (`*`) operator at the e
 | Browse       | `bool` | When set to true, enables directory browsing.                                                                             | `false`                  |
 | Download       | `bool` | When set to true, enables direct download.                                                                             | `false`                  |
 | IndexNames       | `[]string` | The names of the index files for serving a directory.                                                                             | `[]string{"index.html"}`                  |
-| CacheDuration       | `string` | Expiration duration for inactive file handlers.<br /><br />Use a negative time.Duration to disable it.                                                                             | `10 * time.Second`                  |
+| CacheDuration       | `time.Duration` | Expiration duration for inactive file handlers.<br /><br />Use a negative time.Duration to disable it.                                                                             | `10 * time.Second`                  |
 | MaxAge       | `int` | The value for the Cache-Control HTTP-header that is set on the file response. MaxAge is defined in seconds.                                                                             | `0`                  |
 | ModifyResponse       | `fiber.Handler` | ModifyResponse defines a function that allows you to alter the response.                                                                             | `nil`                  |
 | NotFoundHandler       | `fiber.Handler` | NotFoundHandler defines a function to handle when the path is not found.                                                                             | `nil`                  |