Gitified version of the Latest Tweets Widget published in the official Wordpress plugin directory:
http://wordpress.org/plugins/latest-tweets-widget/
Please report issues in the Wordpress plugin directory support forum:
http://wordpress.org/support/plugin/latest-tweets-widget
Note that the actual name of the plugin is "latest-tweets-widget" not "wp-twitter-widget". It's renamed on Github to differentiate it as a Wordpress plugin.
Add the plugin to your Wordpress project via Git as follows:
$ git submodule add https://github.com/timwhitlock/wp-twitter-widget.git \
wp-content/plugins/latest-tweets-widget
If you want to use a stable release listed in the Wordpress plugin directory, you can checkout by tag, e.g.:
$ cd wp-content/plugins/latest-tweets-widget
$ git fetch origin
$ git checkout tags/1.1.0
For further details on the plugin, please visit the official plugin page.