From https://github.com/seaofclouds/tweet:

Important note about Twitter's API changes in 2013

Twitter has discontinued its unauthenticated v1.0 API, so this widget has stopped working as of 2013-06-11.

Twitter wants your only option for on-page widgets to be their own Embedded Timelines, but there are workarounds which involve installing server-side code to support this widget.