upgrade alpine base image to v3.15.0 including tor package upgrade from v0.4.5.10-r0 to v0.4.6.7-r1 (see below)
https://web.archive.org/web/20211204112320/https://gitweb.torproject.org/tor.git/plain/ChangeLog
https://git.alpinelinux.org/aports/commit/community/tor?h=3.15-stable&id=01351ec5162a1c190361b3799c63862a4c94d935
https://git.alpinelinux.org/aports/commit/community/tor?h=3.15-stable&id=7d4f77837c3a2f1cecfbfbe9224552b3614e3664
https://git.alpinelinux.org/aports/commit/community/tor?h=3.15-stable&id=8c36ff0a65aac9960da5cfce6694eedd8d869da6
https://git.alpinelinux.org/aports/commit/community/tor?h=3.15-stable&id=82d7315dd0e5b8d8fca73c175c95c280d24707b1
https://github.com/fphammerle/docker-tor-obfs4-bridge/commit/ebf4ab28c1c9a3b481334feff9826e2f0e2b5cc1