the reason is because although 2.1.20 is the “stable” release, there was a recent security change in openssl that makes it very unresposive and almost impossible to use. so if you have updated openssl thru one of the “pushed” security updates, you’ll need this newer version that is patched for it.
delete all files in the /etc/tor/. directory prior to installing the new version to assure that your old config files are not reused.
i don’t recall if the torrc file must be modified to run, but the important entries are:
SocksPort 9050 # what port to open for local application connections
SocksListenAddress 127.0.0.1 # accept connections only from localhost
if these lines are commented out (preceded by a #) then the # must be removed.
tor will have to be restarted after modifications are made to torrc.