Update for duo@0.8.4

The Duo team made some [minor API changes in 0.8.4](https://github.com/duojs/duo/commit/faf6c4eb4b301418ce382e56d83dba89d422ba1a#diff-450c0af48adb0bb9a0c2b0dd2a8a0110L193) that broke this plugin. This PR makes it work again and bumps the version to v0.0.4.