Improve types of serveStatic's option parameter.

* index accepts a new index string or an array of string.
* maxAges accepts a string accepted by the ms module.

serve-static/serve-static.d.ts

@@ -49,7 +49,7 @@ declare module "serve-static" {
          * By default this module will send "index.html" files in response to a request on a directory.
          * To disable this set false or to supply a new index pass a string or an array in preferred order.
          */
-        index?: boolean;
+        index?: boolean|string|string[];
 
         /**
          * Enable or disable Last-Modified header, defaults to true. Uses the file system's last modified value.
@@ -59,7 +59,7 @@ declare module "serve-static" {
         /**
          * Provide a max-age in milliseconds for http caching, defaults to 0. This can also be a string accepted by the ms module.
          */
-        maxAge?: number;
+        maxAge?: number|string;
 
         /**
          * Redirect to trailing "/" when the pathname is a dir. Defaults to true.