FreshRSS uses a forked version of SimplePie, with a number of patches.
See the read-me of our fork.
Some of the libraries in this folder can be updated semi-automatically by invoking:
cd ./FreshRSS/lib/
composer update --no-autoloader
Remember to read the change-logs, proof-read the changes, preserve possible local patches, add irrelevant files to .gitignore
(minimal installation), and test before committing.