Update to rTorrent stickz v6.1

## Version 6.1 Release
This release resolves two reported software crashes and reverts to the `__builtin_popcountll` wrapper for compatibility across platforms.

## What's Changed
* Update README.md by @WagnerGMD in stickz/rtorrent#46
* libtorrent: Use __builtin_popcountll for compatibility by @stickz in stickz/rtorrent#49
* Fix two SIGPIPE crashes by @stickz in stickz/rtorrent@c9f61f1 and stickz/rtorrent@f391442

## New Contributors
* @WagnerGMD made their first contribution in stickz/rtorrent#46

**Full Changelog**: stickz/rtorrent@v6.0-0.9.8-0.13.8...v6.1-0.9.8-0.13.8

Dockerfile

@@ -11,8 +11,8 @@ ARG GEOIP2_PHPEXT_VERSION=1.3.1
 ARG RUTORRENT_VERSION=31c8d351002fb1bdcd71c0652aa516384d330712
 ARG GEOIP2_RUTORRENT_VERSION=4ff2bde530bb8eef13af84e4413cedea97eda148
 
-# v6.0-0.9.8-0.13.8
-ARG RTORRENT_STICKZ_VERSION=f6ef811e50d78c041dd9865698186a2319b3ef88
+# v6.1-0.9.8-0.13.8
+ARG RTORRENT_STICKZ_VERSION=7e852c88465682864ef80d86f1d085d932ef3d89
 
 ARG ALPINE_VERSION=3.19
 ARG ALPINE_S6_VERSION=${ALPINE_VERSION}-2.2.0.3