`check(CLI::ValidIPV4)` Does Not Account For Trailing Period

[adachng]

Description

If I have the code:

        CLI::App app;

        std::string address_str;

        app.add_option("-a, --address",
                       address_str,
                       "IPv4 address of server")
            ->required()
            ->check(CLI::ValidIPV4);

and I run the app with ./main -a 127.0.0.1., the validator allows this when this is not a valid IPv4 address.