Vary: Accept-Encoding?

In version 1.6.6 I got this when tested on https://gtmetrix.com

The following publicly cacheable, compressible resources should have a "Vary: Accept-Encoding" header:
http://static.addtoany.com/menu/page.js
http://static.addtoany.com/menu/svg/icons.14.svg.css

I dont know if it is an issue that needs to me corrected or not.

https://ww.wp.xz.cn/plugins/add-to-any/