Allow hex for ipv6 literal addr in redirect (#1859)

Co-authored-by: jaredhuang <jaredhuang@tencent.com>

httplib.h

@@ -7275,7 +7275,7 @@ inline bool ClientImpl::redirect(Request &req, Response &res, Error &error) {
   if (location.empty()) { return false; }
 
   const static std::regex re(
-      R"((?:(https?):)?(?://(?:\[([\d:]+)\]|([^:/?#]+))(?::(\d+))?)?([^?#]*)(\?[^#]*)?(?:#.*)?)");
+      R"((?:(https?):)?(?://(?:\[([a-fA-F\d:]+)\]|([^:/?#]+))(?::(\d+))?)?([^?#]*)(\?[^#]*)?(?:#.*)?)");
 
   std::smatch m;
   if (!std::regex_match(location, m, re)) { return false; }