A few days back Nutanix released a minor update to their 5.5 released which was GA 4 December 2018. Read more about the 5.5 release This means the most current version of AOS is now AOS 5.5.0.2.
The 0.0.0.2 is obviously just a minor update which fixes a potential upgrade issue so as usual read the release notes and see if the most current release brings features and or functionality that your specific environment will benefit from.
In addition to AOS 5.5.0.2, Prism Central 5.5.0.2 was also released.
Useful links