update to use package:web

We should update this package to use APIs from package:web; see:

```
   info - lib/src/request/async_xhr_request_client.dart:2:1 - 'dart:html' is deprecated and shouldn't be used.
   Use package:web and dart:js_interop instead.
   Try replacing the use of the deprecated member with the replacement. - deprecated_member_use
```
