XSS vulnerability in serveDir API of @std/http/file-server on POSIX systems

The Deno Standard Library provides APIs for Deno and the Web. Prior to version 1.0.11, `http/file-server`'s `serveDir` with `showDirListing: true` option is vulnerable to cross-site scripting when the attacker is a user who can control file names in the source directory on systems with POSIX file names. Exploitation might also be possible on other systems but less trivial due to e.g. lack of file name support for `<>` in Windows. Version 1.0.11 fixes the issue.