Ubuntu20 Shadowsocks_install

1. fix Python version from "apt_depends=( gettext build-essential unzip gzip python python-dev python-setuptools curl openssl libssl-dev autoconf automake libtool gcc make perl cpio libpcre3 libpcre3-dev zlib1g-dev libev-dev libc-ares-dev git qrencode )" to "apt_depends=( gettext build-essential unzip gzip python3 python3-dev python3-setuptools curl openssl libssl-dev autoconf automake libtool gcc make perl cpio libpcre3 libpcre3-dev zlib1g-dev libev-dev libc-ares-dev git qrencode ")

2. fix /usr/local/shadowsocks/lru_cache.py from "class LRUCache(collections.MutableMapping):" to "class LRUCache(collections.abc.MutableMapping):"

3. ln -s /usr/lib/libsodium.a /usr/lib/liblibsodium.a

then running.