shadowsocks-libev: bump to version 3.1.0

Notable changes since 3.0.8

    ede744a: depends on libcares now instead of libudns
    1c64829: new cmdline option --no-delay for not turning off TCP_NODELAY
    9201619: ss-local: check if client supports socks5 protocol and no-auth-required method
    f8283fc: Fix potential buffer overflow when parsing json config
    380fddb: redir: fix conversion from DSCP to ToS

The two patches are now in the offical repo