It seems that the information you found is outdated, and the latest version of the ANT PluginLib may not be available in the mentioned sources. To obtain the latest version of the ANT PluginLib, I recommend reaching out to the ANT+ organization directly.
As an "Ant Plus Adopter" level member, you should have access to the member-only releases section on the ANT+ developer resources website. You can visit the following URL for more information on accessing member-only releases:
http://www.thisisant.com/developer/resources/downloads/snake game
By accessing the member-only releases section, you should be able to find the latest version of the ANT PluginLib in the appropriate format, such as the .aar file you mentioned (e.g., "antpluginlib_3-8-0.aar"). If you encounter any difficulties or have further questions, I recommend contacting the ANT+ organization directly for assistance.